Operator

An operator, also known as a moderator, is a player designated by admins or other operators to moderate a multiplayer server. This is done to help keep control of the server from unruly players and griefers, and even reward trusted players. Players are assigned as operator by using the command, or by editing the ops text file (ops.txt) in the server directory, then restart the server. Operators have access to a variety of server commands, which aid them in their policing duty. These are activated by typing them into the chat with the appropriate arguments.

Operators are also granted the privilege of destroying and placing blocks within the spawn area. However, admins can manage whether to allow or deny this privilege.

Problems with untrustworthy operators
Operators have access to all commands, meaning they can stop the server, exploit commands, change game modes, and kick/ban players including the admins and server owners. This can be avoided in modded servers with a permissions plugin, which allow particular users to only access specific operator commands.

On SMP servers, untrustworthy operators can also be tempted to go into creative mode. This can result in griefing, an unfair balance, and disagreement among players. Once again, this can be combated using a permissions plugin.

Operators are also able to edit command blocks, so be wary that they may be changed by untrustworthy people.