Bots are AI-controlled player characters standing in the place of real players.

A bot (short for robot) is similar to an NPC in a multiplayer game, usually designed to behave like a human-controlled player.

Given the team-based competitive nature behind many first-person shooters, these games usually come with bots for the player to play with/against in an offline game, in order to benefit users with limited or no internet access.

Another distinct definition of bot is that of a computer program which is commonly designed to perform monotonous or hard-to-achieve tasks such as "farming" and raising levels in RPG-type games. As a result, most RPG games have banned them from use because it is considered cheating. In FPS games this type of bot is also known to be a form of cheating. It helps players achieve better scores by improving their aim and reflexes which, in the extreme case, are completely controlled by the bot software.

Bot
Server-Side Bots
Computer game bot[en.wikipedia.org]