Edit conflict

See Wikipedia:Edit conflict for more information about this topic as it pertains specifically to Wikipedia.

An edit conflict occurs when a shared document is being edited by more than one person at the same time and a conflict is generated. One person attempts to edit the document, but upon trying to save the new version, another person has already modified the document in the intervening time period, thus causing a difference between the attempted edit and the already-made edit that must be resolved manually.

A similar problem can occur when two or more users simultaneously edit the same file in a revision control system that does not have file locking. See Concurrent Versions System.