Torrent trackers. Basically the index that let's your search for and find torrents, private ones are invite only. Common for rare music or better sources of films, and so on.

Not that stupid, considering the word Torrent doesn't appear above the fold. Took me a while to figure out as well.

A "private tracker" is basically a speakeasy for media piracy.

It's BitTorrent, so it's peer-to-peer, but it's exclusive and secretive to avoid letting in surveillance bots that get everyone threatening letters from their ISPs.