All users who have the torrent open make up what is called a swarm. Technically, a seeder is someone who has 100-percent of the pieces that make up the torrent. Initially, the first few leachers within a swarm feed off the seeder.The more seeders the faster the download will go.    Leechers are people who has a negative effect on  the swarm of the torrent. Leechers are commonly the users who  download much than they upload.