Tracker

A tracker refers to a BitTorrent tracker, a server that allows communication between peers that are using the BitTorrent protocol. The tracker's job is to keep track of where copies are located, determine if the files are available, and coordinate the transferring of files between users.

If a BitTorrent tracker is shut down or fails, users wishing to communicate with one another will find they're unable to since they are required to listen to the trackers instructions before they can determine what to do.

There are two kinds of trackers, public and private. Public trackers are far more popular then their private counterpart however this is mostly due to lack of awareness as well as troubles getting into private trackers.