This page in a nutshell: Edit conflicts occur when two users make edits to the same page at the same time, causing the edits to conflict with each other. When this happens, the MediaWiki software provides a screen that allows the user to resolve the conflict manually.
This page discusses edit conflicts, and how to deal with them. To understand what an edit conflict is, consider the following situation:
Bob clicks "Edit source" on a page. The software sends Bob the current revision of the page, #123.
Alice clicks "Edit source" on the same page, while Bob is editing. The software sends Alice the current revision of the page, #123.
Bob finishes his edits and clicks "Publish changes". The software saves Bob's edits as revision #124, and publishes #124. Alice is still editing #123.
Alice finishes her edits and clicks "Publish changes". The software saves Alice's edits as revision #125, but discovers that #125 is based on revision #123, although the currently published revision is #124. The software tries to automatically reconcile the differences, but fails. Alice therefore gets an "edit conflict" page, giving Alice a chance to reconcile the differences between #124 and #125 manually.
