This glossary of common torrenting terminology will help you understand the basics of BitTorrent. This is a work in progress, so if we’ve missed something make sure to let us know in the comments.
The number of complete copies of a file. Each seeder adds 1 to the number of available copies. Leechers with incomplete copies can add partial numbers (like 0.36) to the availability.
Client / Torrent Client
Your Client is the software that manages your BitTorrent connections. It is responsible for loading torrent links and connecting to peers in the swarm. Many torrent clients add extra functionality like encryption, proxy support, and bandwidth management.
Popular torrent clients include: uTorrent, BitTorrent, Vuze, Deluge, QBittorrent, and Transmission.
When the swarm doesn’t have all pieces necessary to complete the torrent, it’s considered a Dead Torrent. Sometimes torrents can rise from the dead if a seeder with the complete file comes back online. Others will never recover.
BitTorrent is a decentralized protocol. Instead downloading files from a central server, pieces of torrent files are distributed throughout the network, making it more resilient censorship-proof.
Distributed Hash Table (DHT)
Instead of loading a list of peers directly from a Tracker, DHT allows your torrent client to discover new peers from other peers you’ve already connected to. It’s like a referral from a friend. DHT helps keep the BitTorrent network decentralized so trackers aren’t a point of failure.
Encryption is a method of scrambling data so that it cannot be read by 3rd-parties. Most torrent clients have optional protocol encryption which can be used to disguise torrent traffic and circumvent throttling.
A fake torrent is any torrent file with a deceptive title, one that doesn’t match its contents. Often fake torrents are extremely popular or rare media files such as images, videos or music. Fake torrents may be just be a harmless Rickroll, or could contain malware, spyware and viruses.
A firewall is type of security software that limits incoming/outgoing connections to a device or network. It is designed to control access and prevent dangerous network activity (like hackers). Firewalls can be run at the system-level (Windows Firewall on your PC) or Network level (your ISP’s firewall). Some firewalls may block BitTorrent ports or peer connections.
Before the actual content of a torrent file can be downloaded, you have to grab the metadata which contains information like the number of pieces, file list, and torrent hash.
Each .torrent file has a unique hash, which is like a digital fingerprint. The hash is a method of authenticating the integrity of data, so malicious peers can’t change a piece of the file.
Hit and Run
This is a pejorative term used to describe peers who download the file while seeing as little as possible (hit), then immediately stop seeding once the file is complete (run).
A leech is any peer that doesn’t have a complete copy of the torrent file and is still downloading. It also refers (negatively) to anyone who hits-and-runs or rarely seeds. You can be both leecher and seeder simultaneously, by uploading the pieces of the file you’ve already downloaded.
Magnet Links are basically a URL (hyperlink) with extra parameters that point to a .torrent file (the metadata with file information). Most major torrent clients can open magnet links, authenticate the .torrent file by the magnet’s hash, and grab the torrent directly.
Many Internet Service Providers (ISP) use sophisticated technology to limit the amount of bandwidth subscribers can use for p2p filesharing technologies like BitTorrent. You can also throttle your own torrent downloads with a protocol like uTP (in uTorrent) or by manually adjusting the bandwidth limits for individual torrents. Throttling can be defeated with encryption.
P2P is an abbreviation for peer-to-peer, which describes the way the BitTorrent network functions. Instead of routing connections through a central sever, each torrent peer is both the client and server for pieces of the torrent file.
Each individual node running a BitTorrent client is a peer. Both seeders and leechers can be peers (though sometimes peer is used in a manner that refers to a client that is still leeching the file.
‘Peer’ in this instance keeps some of its traditional meaning, as each node on a p2p network is equal in terms of hierarchy.
A Proxy is a remote web server that can connect to a torrent swarm or tracker on your behalf. It can be used to get through firewalls or hide your IP Address. Many clients have built-in proxy support.
Private Trackers are invite-only torrent communities that enforce specific rules and share ratios. They offer a bit more privacy from torrent monitoring than public trackers do. They also tend to have well-seeded files and many hard-to-find torrents that aren’t available publicly. Many private trackers are organized around a specific theme (live music bootlegs for example).
A seed is any peer that has a complete copy of the torrent file and is currently uploading pieces to the swarm. Seeding is the act of uploading. Peers with only part of a torrent file can be seeders of their completed portion while leeching the remainder.
There is an unwritten rule that you should seed at least as much data as you leech for each torrent file (share ratio of 1). This improves the overall health of the network and prevents unseeded torrents (which can’t be completed because no peer has a complete copy.
The Share Ratio is a measure of how much you contribute to the swarm relative to how much you take. It is calculated for each torrent file.
Share Ratio = Uploaded data / Downloaded data
Ideally, each peer should keep seeding until they achieve a share ratio greater than 1.0.
A swarm is the sum total of all peers (seeders + leechers) sharing a torrent file.
A torrent tracker is a central server that tracks the number and location of peers in a particular torrent swarm. The torrent client periodically sends a report to the tracker and return receives an updated status of all peers for that torrent.
DHT, by contrast, is a ‘trackerless’ method of discovering peers.