Bot

MediaWiki.org wiki has a page about this at:

A bot (short for software robot) is an automated software program used to perform certain repetitive tasks on a wiki. Bots typically require approval to operate, and are occasionally used by vandals to cause extensive damage to a wiki's content in a short period of time.

Special:ListUsers/bot produces a list of all accounts which are member of the “Bots” user group . Additionally, "bot" is a user right. Edits by a user with this “right” (read: property) do not show up in recent changes by default. Typically, a user from the group "Bots" will have the "bot" user right. User rights are often called "flags" and bots with user right "bot" are often called "flagged" bots.

Running your own bot

See Manual:Creating a bot on mediawiki.org for full instructions.

Using Pywikibot
English Wikipedia bot policy
Steward requests/Bot status — to request an account be marked with a bot flag (for wikis without any active bureaucrat)
Setting bot access — information for people running their own MediaWiki installation. Can be changed at Special:UserRights
wikitech:Help:Toolforge/Developing successful tools — best practices for all bot-owners

Miscellaneous bot pages

Bot policy
Small wiki toolkits/Starter kit/Bots and Tools — list of popular and useful bots on Wikimedia wikis
Vandalbot — advice on dealing with malicious bots
Rollback — includes instructions for using "bot rollback" to hide vandalism from recent changes

Frameworks and interfaces for bot development

See mw:Manual:Creating a bot#Programming languages and libraries for lists.