What is Bittorrent?

Introduction
Bittorrent is a decentralized peer to peer distribution of content which uses the upload bandwidth of each individual who is downloading the content, and those who have downloaded, to transfer the content.

Definitions Of Common Bittorrent Terms
Definitions of common bittorrent terms in simple (hopefully) language.

Torrent - A small text file that contains information about specific (associated) content and about tracker(s).

Torrent Search Site - A site that indexes torrent files and their associated content.

Tracker - A communications hub that helps people active on a torrent connect to each other.

Bittorrent Client - A program that opens torrent files to transfer of the content associated with the torrent.

Seeds - Those who have 100% of the torrent's associated content and are uploading to Peers (Leechers).

Peers - Two definitions.

1. Those who have less than 100% of the content associated with the torrent.  They download from seeds and other peers and upload to other peers. (Most bittorrent clients use the term this way).
2. All of those active on a torrent, i.e., those who have 100% and those who have less than 100%. (Most torrent search sites use this definition).

Leechers - Two definitions

1. Those who have less than 100% of the content.  They download from seeds and other leechers and upload to other leechers. (Most torrent search sites use this term).
2. Those who download 100% of a torrent's associated content, but do not upload back at least 100% of that content. (Used by all.  Ths negative connotation is why bittorrent clients use peers for the above definition.)

Ratio - The amount uploaded divided by the amount downloaded.  Usually shown per torrent and overall. 

Swarm - The group of people active on a single torrent. (Same as definition 2 of Peers, above)

DHT - Short for Distributed Hash Table.  A way of connecting to other users without the tracker being involved.  Especially useful when a tracker goes down or for hosting trackerless torrents.

PEX - Short for Peer Exchange. A way of connecting to other users without the tracker, through people that you are already connected to.  Especially useful if tracker is down.

Encryption - Primarily designed to help users avoid interference from an Internet Service Provider (ISP).

How It Works
This is a non-technical description of the bittorrent process.

A user goes to a torrent search search site to search for content.  When the user finds wanted content, the user downloads the .torrent file associated with the content.  When the torrent is opened in a bittorrent client, transfer of the associated content begins.

The bittorrent client communicates to a tracker through the information contained in the .torrent file.  A tracker essentially serves as a communications hub for this swarm of individuals, helping them find each other.  DHT and PEX also help users to find each other.

Bittorrent works by splitting content files into hundreds of smaller “bits” and sharing those bits, using the upload bandwidth of the active users, across a swarm of linked users.  These bits are downloaded randomly, so the content is generally not useable until the download is complete.  The bittorrent client will reject any bits that do not match the information contained in the torrent file.  This ensures that the completed download will be an uncorrupted copy of the content.

Conclusion
Hopefully this article has given you a basic understanding of the bittorrent process.  If you have any questions, or comments, feel free to post below and I will try to address them.
From its inauspicious start in 2001, bittorrent has grown to one of the major forces on the internet.  Estimates of bandwidth use by bittorrent are one third, and upwards, of all internet use.
There are presently over 3 million torrents active and over a petabyte of content associated with those torrents.
To get started in bittorrent, see the Related Links below.

Related Links

• Best Free Bittorrent Client
• Searching for Torrents (Popular Torrent Search Sites)
• Finding Legal (and Free) Torrents
• Optimizing Bittorrent Clients for Speed