In torrenting, a “seeder” is the name for a peer on the P2P network who has the completed file for a torrent and is continuing to share that file. A “leecher” is the name of a peer on the network for someone who is torrenting the file from the seeders — they are “leeching” from them. Leechers also seed the parts of the file they have already downloaded as they leech the rest of the parts from others. The more seeders there are for a torrent, the faster you can expect to complete that torrent, as there are more people you can accept pieces of the file from.