In the context of torrenting, a tracker is a server that keeps track of the peers (users) who are sharing a particular torrent file. When you download a torrent file, your client (e.g., uTorrent, BitTorrent, or qBittorrent) connects to the tracker to get a list of available peers who are sharing the same file. The tracker then facilitates communication between your client and the peers, allowing you to download the file in chunks from multiple sources.
Here's a step-by-step explanation of how trackers work: trackers for torrent
These are open to everyone. Sites like The Pirate Bay, 1337x, or RARBG (RIP) utilize public trackers. In the context of torrenting, a tracker is