Glossary of Common Bittorrent Terminology

Announce

Same as "scrape" (below), but the client also announces that it wants to join the swarm and that the server should add it to the list of peers in that swarm.

Availability

(AKA distributed copies.) The number of full copies of the file available to the individual client. Each seed adds 1.0 to this number, as they have a complete copy of the file. A connected peer with only a fraction of the file available adds that fraction to the availability, if no other peer has this particular part of the file. Example: a peer with 62.5% of the file downloaded increases the availability by 0.625. However, if two peers have the same portion of the file downloaded – let's say 50% - and there is only one seeder, the availability would be 1.5.

Choked

Describes a peer to whom the torrent client refuses to send file pieces. A client might choke another client in several situations:
  • The second client is a seed, in which case it does not want any pieces of the file (it is completely uninterested).
  • The client is already uploading at its full capacity (it has reached the value of "maximum uploads")
  • The second client has been blacklisted perhaps for being abusive or is using a blacklisted bittorrent client.
  • Client

    The program that enables p2p file-sharing utilizing bittorrent protocol. Examples of clients include uTorrent, Bittorrent and Vuze.

    Downloader

    A downloader is any peer who does not have the entire file and is downloading the file. This term lacks the negative connotation attributed to leech. In Bram Cohen's bittorent vernacular, he prefers downloader to leech because bittorrent's tit-for-tat protocol ensures that downloaders also upload and thus do not unfairly qualify as leeches.

    End Game

    Bittorrent has a couple of download strategies for initializing a download, downloading normally somewhere in the middle of the torrent, and typically, the last download pieces arrive more slowly than the others since the faster and more easily accessible pieces should have already been obtained. So, to prevent this, the bittorrent client attempts to get the last missing pieces from all of its peers. Upon receiving a piece, a cancel request command is sent to the other peers.

    Fake

    A fake is a torrent that does not contain what is specified in its name or description (i.e. a torrent said to contain a video, but it contains perhaps only a snapshot of a moment in the video, or in many cases a virus).

    Hash

    The hash is the string of alphanumeric characters in the .torrent file that the client uses to verify the data being transferred. It contains information like the file list, sizes and pieces, etc. Every single piece received is first checked against the hash. If it fails verification, the data is discarded and then requested again. The "Hash Fails" field in the torrent's General tab indicates the number of these hash fails. Hash checks can greatly reduce the chance that invalid data is incorrectly identified as valid by the bittorrent client, but it is still very possible for invalid data to have the same hash value as the valid data and be treated as such. This is known as hash collision.

    Health

    Health is usually shown in a bar or in "%" next to the torrents name and size, on the site where the .torrent file is hosted. It shows if all pieces of the torrent are available to download (i.e. 50% means that only half of the torrent files are available).

    Index

    An index is a list of .torrent files (usually including descriptions and other information about the file) managed by a website and made available for searches. An index website may also be a tracker.

    Interested

    Describes a downloader who wishes to obtain pieces of a file that the client possesses. For example, the uploading client would flag a downloading client as "interested" if the client did not possess a piece that it did, and wished to obtain it.

    Leech

    A leech is a term with two meanings. Usually it is used to refer a peer who has a negative effect on the swarm by having a very poor share ratio (downloading much more than they upload). Most leeches do not leave their bittorrent client open to seed the file after their download has completed. However, some leeches intentionally avoid uploading by modifying clients or excessively limiting their upload speed. The often used second meaning of leech is synonymous with downloader (above): It is used simply to describe any peer or any client that does not have 100% of the data.

    Lurker

    A lurker is a user that only downloads files from the group but does not add any new content. Unlike a leech, a lurker will likely seed what he has downloaded.

    P2P

    Stands for "peer to peer". This is the technology used for file sharing among computer users over the internet. In a p2p network, each node (or computer on the network) acts as both client and server. In other words, each computer is capable of both receiving and sending data.

    Peer

    A peer is one instance of a bittorrent client running on a computer connected to the Internet to which other clients connect and transfer data. Usually, a peer does not possess the complete file, but only parts of it. However, in the colloquial definition, "peer" may be used to refer to any participant in the swarm (in this case, it is synonymous with "client").

    Piece

    This refers to the torrent files being divided up into equal specific sized pieces (example 512Kb, 1Mb). The pieces are distributed randomly among peers in order to optimize trading efficiency.

    Ratio credit

    A ratio credit, also known as an upload credit, is a currency system used on a number of private trackers to provide incentive for higher upload/download ratios among member file-sharers. In such a system, those users who have greater amounts of bandwidth, hard drive space (in particular, seedboxes) or idle computer uptime are at a greater advantage to accumulate ratio credits versus those who are lacking in any one or more of the same resources.

    Scrape

    This is when a client sends a request to the tracking server for any and all information about the statistics of the torrent, such as with whom to share the file and how well those other users may be sharing.

    Seeder

    A seeder is a peer that has a complete copy of the torrent and offers it for upload. The more seeders there are, the better the chances of getting a high download speed. If the seeder seeds the whole copy of the download they should theoretically get faster downloads

    Share ratio

    A user's share ratio for any individual torrent is a number determined by dividing the amount of data uploaded by the amount of data downloaded. Final share ratios over 1.xx carry a positive connotation in the bittorrent community because they indicate that the user has sent more data to other users than they received. Likewise, share ratios under 1 have a negative connotation.

    Snubbed

    An uploading clien is flagged as snubbed if the downloading client has not received any data from it, usually in over 60 seconds.

    Super-seeding

    When a file is brand new, much time can be wasted because the seeding client might send the same file piece to many different peers, while other pieces have not yet been downloaded at all. Some clients, like Vuze, BitTornado, and uTorrent have an integrated "super-seed" mode, where they try to only send out the pieces that have never been sent out before, theoretically making the initial propagation of the file significantly faster. However, super-seeding becomes substantially less effective and may even reduce performance as compared to the normal "rarest first" model in cases where some peers may have poor or limited connectivity. This mode is generally used only for a brand new torrent, or one which must be re-seeded because no other seeds are available.

    Swarm

    Together, every peer (including seeders) that are sharing a torrent are called a swarm. For example, six ordinary peers and four seeders make a swarm of ten.

    Torrent

    A torrent can mean either a .torrent metadata file or all the files described by it, depending on context. The torrent file contains metadata about all the files it makes downloadable, including their names, sizes and checksums of all pieces in the torrent. It also contains the address of a tracker that coordinates communication between peers in the swarm.

    Tracker

    A tracker is a server that keeps track of what seeds and peers are in the swarm. Clients report information to the tracker periodically and in exchange receive information about other clients to which they may connect. The tracker is not directly involved in the data transfer and does not possess a copy of the file.