Torrent terminology
What do all those words mean?
Seed is an user, which has the file completely downloaded and is sharing it.
Peer is every downloading user, that doesn't have the file complete. After finishing the download becomes a seed.
Leech is practically the same as peer, sometimes it is a label for a peer with a very low UD ratio.
UD ratio is a rate between received and sent amount of data. It is modest to keep this at least on the value 1 (share the same amount you download)
Tracker is a server, that co-ordinates downloading of all users.
Swarm is a summary of all seeds and peers (so everybody connected to the tracker makes swarm).
Continue: torrent legality - is it legal to download with torrents?
