Glossary

Especially if you're new to BitTorrent in general, there are probably many new and unfamiliar terms used throughout this manual (and in many other BitTorrent-related places). To help "clue" you in on the new vocabulary, this glossary can be of great help.

A

announce: The act of connecting to a tracker to update it on your status, and to obtain information from it as well, including (but not limited to) an updated peer list.
availability: The number of complete copies of the torrent contents there are distributed in the part of the swarm you're connected to. The amount of the torrent contents you currently have is included in the availability count. A swarm with no seed and with an availability below 1.0 will likely be unable to finish transferring the complete torrent contents.

B

block: The units of data that comprise a piece. Because blocks do not directly affect whether torrent contents are considered to be finished transferring, it is not seen as an appreciable unit of data with regards to BitTorrent like the piece is.
byte: A unit used for measuring the size of data on a computer storage device. Many people confuse "byte" for "bit" when referring to speeds. A byte is composed of 8 bits, so there is a clear distinction, and terminology should not be confused when referring to bytes.
broadcatching: The act of downloading content from an RSS feed.

C

choked: This word describes the state of a BitTorrent connection. When a connection is choked, it means the person who is supposed to be doing the uploading on the connection does not want to send anything. This generally happens when the uploader's upload slots are full.
client: The application a user is using when connected to a swarm. In this case, the application being used to connect to swarms is µTorrent, so it is the client.

D

DHCP (Dynamic Host Configuration Protocol): A protocol that allows networked devices to be assigned an unique IP address automatically from a pool of unused IP addresses.
DHT (Distributed Hash Table): A distributed tracker that works similarly to a regular tracker in that you announce to it and get back a list of peers that are transferring the same .torrent file as you. Because DHT is distributed, there is no single point of failure, so even if a single node disconnects from DHT, the tracker will continue to work (unlike with normal trackers, where if the server goes down, it becomes unusable). DHT can be thought of as a backup tracker.
disk cache: A feature that makes use of available memory to stores data for quicker access as well as ease disk thrashing. The use of a disk cache will cause an increase in memory usage in return for improved performance.
disk thrashing: When a storage disk gets accessed very frequently. Extended disk thrashing may lead to hard drive wear and tear, shortening a drive's life.
double NAT: A situation where the network device is behind more than one NAT devices (generally routers). In this situation, forwarding ports from just one of those NAT devices is generally insufficient, and more actions need to be taken as described in the advanced port forwarding guide.
download: The act of transferring data from another computer onto your own.

E

encryption: The obfuscation (concealing) of data behind seemingly random data in order to hide its true identity.
endgame mode: A change in the piece requesting strategy that occurs when a download is near completion during which the client requests pieces from all connected peers rather than requesting a piece from one peer at a time in the normal operating mode. Endgame mode is used because download rates often slow down considerably as a torrent job nears completion due to the tendency for the remaining pieces to be downloaded from peers with saturated connections. By requesting data from all peers rather than waiting for a single peer, such a bottleneck can be bypassed. This mode is not used during normal operating modes because of the large amount of overhead it potentially generates in sending requests to all peers.
ephemeral port range: A range of port numbers automatically allocated by the operating system for use by any application on the system with network access. Ports in the ephemeral port range are typically used to make temporary outgoing connections. The default ephemeral port range is configurable via the Windows Registry, and may vary from (operating) system to (operating) system. More about the ephemeral port range can be learned on Wikipedia's Ephemeral Ports article and its external links.

F

firewall: A barrier (hardware and/or software) that prevents communication to and/or from certain computers, depending on the rules set in the firewall.

G

GiB (gibibyte): A gibibyte is equal to 1024 MiB. Most people are referring to "gibibyte" when they say "gigabyte," although that is technically an incorrect usage of terms.

H

half-open connection: A connection that is not fully established on both ends. Half-open connections occur when you attempt to connect to an IP address, but the IP address hasn't yet responded.
hash: A "fingerprint" of data assumed to be unique to the data. Because of the assumed uniqueness of the data, it is used to verify that a piece of data is indeed uncorrupted (since the corrupted data's hash would not match its expected hash).
hash check: The comparing of a piece of data's hash with a reference hash in order to verify the integrity of the piece of data.
hashfail: When a piece fails the hash check used to verify data integrity.

I

index: A site that lists .torrent files available for download.
Initial Seeding (Super Seeding): A method of seeding that attempts to decrease the bandwidth load for the initial seeder. With normal seeding methods, the initial seeder typically has to upload 150% to 200%, or even more, of the original data in before a full copy of the data has been distributed into the swarm. With initial seeding, the initial seed attempts to get the rarest pieces out instead of uploading identical pieces repeatedly, often lowering the initial upload requirement to 105%. Initial seeding does not necessarily improve upload speeds or decrease seeding time. It should be used only if you are the sole seeder on the swarm, and if there are at least 2 peers connected. Generally, initial seeding should not be used by people with high upload speeds.
interested: This word describes the state of a BitTorrent connection. When a peer is interested, it means the peer is interested in the data that the peer on the other end of the connection has, and is willing to accept data from the other peer.
IP address: A number used to uniquely identify devices on a network.
ISP (Internet Service Provider): The company providing for your Internet service.
ISP throttling: A term used to refer to the throttling of BitTorrent traffic by ISPs.

K

KiB (kibibyte): A kibibyte is equal to 1024 bytes. Most people are referring to kibibyte when they say "kilobyte," although that is technically an incorrect usage of terms.

L

LAN (Local Area Network)

A network of computers in a local area, such as a home.

LAN IP address

The private, internal IP address that locates a computer on a LAN. A LAN IP address is not visible to users outside of the LAN. As described by RFC 1918, the following ranges are designated as reserved IP addresses for private LANs:

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

LPD (Local Peer Discovery)

A method by which µTorrent attempts to discover new peers local relative to your computer's network. Local Peer Discovery makes use of IP multicast.

leecher

A person who downloads, but fails to reciprocate the generosity of others by not sharing back. The word "leecher" carrys a strong negative connotation. Some people use the words "leecher" and "peer" interchangeably, though this practice is not recommended (as it may lead to word confusion).

M

magnet URI: A link that tells the client what files to find and download over DHT.
MiB (mebibyte): A mebibyte is equal to 1024 KiB. Most people are referring to "mebibyte" when they say "megabyte," although that is technically an incorrect usage of terms.
Micro Transport Protocol (uTP): A UDP-based reliable transport protocol designed to minimize latency, but maximize bandwidth when latency is not excessive. This alleviates the bandwidth saturation that often occurs to BitTorrent users while they are transferring data and using the Internet for other purposes.

N

NAT (Network Address Translation): The changing of the source or destination IP address for a data packet. This usually occurs when one is behind a firewall or router, where it translates IP addresses so that multiple computers can exist on a LAN with while using the same WAN IP address.
NAT-PMP (NAT Port Mapping Protocol): An alternative to UPnP created by Apple, Inc. NAT-PMP is not as widely supported as UPnP is, and uptake of the protocol has been limited to Apple, Inc. products only thus far.
NAT Traversal: Techniques of establishing connections that traverse (pass through) NAT gateways. When it works, NAT traversal can help bypass port forwarding issues.

O

optimistic unchoke: When a client tries to start a transfer on a previously choked connection in hopes that the connection becomes unchoked.
overhead: Additional data used and required for communication and coordination between sender and receiver that is not part of the payload data actually being transferred.

P

P2P (peer-to-peer): The use of bandwidth of users using the same peer-to-peer service to perform the functions of the peer-to-peer service or software. Centralized servers are not what keeps P2P networks alive, but rather, the peers themselves.
payload: The actual data being transferred from sender to receiver, not counting overhead.
PE (Protocol Encryption): An specification designed jointly by Azureus and µTorrent developers, created as an attempt to bypass throttling and/or blocking of BitTorrent traffic by ISPs by encryption of the data. There are different methods of encryption, ranging from full encryption of all of the data, to partial encryption of the data (header encryption only, not unlike with PHE, although it's still not as easily detected as PHE).
peer: A user/client connected to the swarm. People sometimes refer to peers as "leechers," though they also use the same word to refer to its more negative connotation. It's recommended that you use the word "leecher" to strictly refer to people who don't share so to keep the distinction clear and confusion to a minimum.
peer list: A list containing the IPs and ports of other peers.
PEX (Peer Exchange): A feature to exchange peer lists with other peers that support the same PEX implementation (generally limited to peers using the same BitTorrent client). By exchanging peer lists, it's possible to find peers not included in the peer list supplied by the tracker.
PHE (Protocol Header Encryption): An old method of encryption created by the BitComet developer that encrypted only a part of the data (the header) in an attempt to bypass ISP throttling and/or blocking of BitTorrent traffic. Because its specification was designed in a relatively poor manner, ISPs were able to detect it with little trouble, rendering it useless.
piece: The smallest appreciable unit of data in BitTorrent. The size of pieces can be different depending on the .torrent file in question.
piece distribution: The general distribution of the pieces across the swarm. BitTorrent is generally most efficient when piece distribution is random, with minimal "clumping" of pieces available in the swarm.
poisoning: The act of intentionally feeding invalid data into the swarm, resulting in hashfails for peers receiving the invalid data. Outfits with (or hired by other entiries with) anti-P2P agendas are the most common sources of swarm poisoning.
port forwarding: The act of passing data on the forwarded port from one network device to another. In most cases regarding BitTorrent, port forwarding refers to the forwarding of connections from a router to a specific computer attempting to listen on that port.
'private' flag: A piece of information stored in a .torrent file that tells any BitTorrent client that recognizes the flag to disable DHT, LPD, and PEX for that specific .torrent. The 'private' flag is typically used in .torrent files served by private trackers as a method of keeping a swarm isolated from people who aren't members of the private tracker.
private tracker: A tracker that requires users to log in to use it. Private trackers typically enforce ratio requirements (by banning users whose ratios are too low) in order to prevent or minimize the leeching that is prevalent on many public trackers.
protocol: A set of rules and description of how to do things. In the case of the BitTorrent protocol, it is a set of rules describing how BitTorrent clients should communicate and transfer data with each other.
proxy: A computer that is told to make a connection to another computer, and relay the data transferred between the two computers to the original computer that connected to the proxy. Essentially, using a proxy is a way to make an indirect connection to another computer by way of the proxy computer.
public tracker: A tracker that is open for anyone to use (as opposed to private trackers, where only people who hold accounts can use the tracker).

R

ratio: A number derived from the division of two other numbers. In the context of BitTorrent, people are normally referring to share ratio when they speak of a ratio.
reseed: The act of rejoining a swarm with no seeds as a seed.
RSS feed: A file that is updated so that it delivers information and content in such a way that allows one to track updates quickly and easily.

S

scrape: The grabbing of statistics (number of seeds and peers) from a tracker regarding a specific swarm.
seed: A peer with 100% of the data in the torrent contents.
seeding: The act of being connected to a swarm as a seed.
share ratio: The ratio of the amount of data you've uploaded to the amount of data you've downloaded.
snubbed: This word describes the state of a BitTorrent connection. A connection is marked as snubbed when the client has not received anything over the connection for an extended period of time.
static IP address: An IP address that does not change (remains static) across multiple sessions. A static IP address is necessary in port forwarding, as ports are usually forwarded to a specific IP address, where the rule does not change even if the computer's IP address does.
swarm: The collective group of peers (which includes seeds) that are connected by a common .torrent file.

T

throttle: A term used to refer to the intentional slowing down of transfer rates (download and/or upload), typically used in the context of ISP throttling.
torrent: A small file containing metadata from the files it is describing. In other contexts, it is sometimes used to refer to the swarm connected around that small file.
tracker: Something that a client connects to in order to share its IP and port, as well as obtain information, including peer lists.

U

upload: The act of transferring data from your computer onto another.
UPnP (Universal Plug and Play): A protocol that allows devices on a network to communicate with each other seamlessly. In the case of µTorrent, UPnP is used to forward a port on a router without the need to open the port manually.

W

WAN (Wide Area Network): A computer network that covers a large geographical area. A WAN connects multiple LANs together. The Internet is an example of a WAN.
WAN IP address: The public, external IP address that users outside of your own network see your network to be located at on the WAN. WAN IP addresses reveal nothing about internal IP address allocation on a LAN located at the WAN IP address.
wasted: Data that is tossed out either because it hashfailed, or because it was redundant data that the client had already downloaded.
web interface (Web UI): An interface for a supported web browser that allows one to control an application remotely.
web seed: A seed that is basically a regular web server hosting the requested file. BitTorrent clients that support web seeds use them like any other seed, and can request data segments from the server much like requesting pieces from an ordinary seed. The use of web seeds ensures that a torrent swarm will never die as long as the file being seeded is left intact on the server and the server does not go down.