Leech

To leech means to join a party or enter a mission and then do nothing. While some people think of leeching as only done maliciously but even a person who joins a party to complete a mission/quest and does nothing because they are AFK is still leeching on the rest of the party.

In addition to the dishonesty involved in reaping the rewards of other people's work and not helping, leechers hurt the party in many way:
 * The party is missing a player, who, if they do nothing else, will share some of the enemy's fire power.
 * The party may have expected this player to perform a specific role needed for the completion of the mission.
 * Often, people will be discouraged by the presence of leechers and tempted to leave.

Unfortunately nothing can be done to protect against leechers, but not being one is the first step.