Leech
Leech may refer to any of the following:
1. With file sharing, a leech or leecher is a person who copies a lot of data but never returns the favor. An example is someone who downloads videos from a P2P service or torrent but doesn't use their computer to share them (or other files) with fellow users.
Some networks that share files may set limits to help prevent leeching. For example, there are services with a system that distributes credits when someone uploads (shares) a file and only allows people to download if they have unused credits.
2. Related to video games, a leech is a player who joins a group of players to get experience or loot without doing anything helpful. Most groups do not like leechers and uninvite them from the group. However, some players sell "leeching" services for gold or other in-game currency. Their services often include taking players through a dungeon or raid, allowing the paying players to get experience or loot without doing anything.