A "bot" is any automated process, program, or script that makes it easier for a user to make tedious or repetitive edits and actions on a wiki. When a bot is running in quick succession, the recent changes log can sometimes be overtaken, making it harder to spot more substantial edits by regular users. Giving an account a "bot flag" will hide these edits from the recent changes list (although any editor can still choose to see them by clicking "Show bots").
On Wikia, a user who wishes to use a bot should set up a separate account for it, then talk with other users on the wiki about whether the types of edits the bot makes should be hidden. After discussing it with the community, the bot owner or admin can request the bot be flagged. A detailed information about bots can be found on Help:Bots
Bot accounts that can perform their tasks across all wikis are tagged as Global Bot.