A bot is a computer program that automatically retrieves or updates wiki pages when it is executed. In general, bots are used for repetitive maintenance tasks, whose volume and characteristics are too large to be performed manually by users.
Developing and executing bots is normally outside the role of normal users, requires programming experience and must be done in coordination with the wiki's admins or other staff.
Bots do not access the wiki through the normal user interface. MediaWiki has an API (Application Programming Interface) available for this purpose. An API is a protocol for standardised communication between two computer programs. Check mw:API:Client code for more information.
Bots used several different frameworks, the most popular being AutoWikiBrowser and PyWikipediaBot. Several bot operators create their own frameworks, for fun or because of the many limitations that existing frameworks have.