The seeders / leechers statistics indicate something like 2(7). I assume that the 2 means that there are 2 seeders, but what does the 7 mean?

7 other (not connected to) seeds in the swarm.

What does it mean for a seed to be in the "swarm" but not connected?

Is there something I can read to learn how torrents work and what the associated terminology means? Unfortunately help for ktorrent doesn't exist.

http://en.wikipedia.org/wiki/BitTorrent_(protocol)

Swarm is a pool of all clients participating in the sharing of the torrent. For many reasons, you usually don't connect to every seed in the swarm.