When do peers build a "swarm" ?

[pstein]

When do peers build a "swarm" ?

For a certain download for example I can read:

Peers: 3 of 11 connected (7 in swarm)

What does that mean ?

[jewelisheaven]

It means you are connected to 3 people of 11 you know of and the tracker(s) returned 7.

If it said seeds, the same would be true except the peers would have 100% under Peers tab.

[Ultima]

A swarm is just the network of peers connected to the torrent; peers don't really build a swarm -- they are the swarm. There's an apparent disconnect between the "7 in swarm" and the actual peers count because the tracker scrape is often inaccurate (and the tracker scrape is where µTorrent gets the 7 from).