The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request.

The server SHOULD generate a payload that includes enough information for a user to recognize the source of the conflict. Conflicts are most likely to occur in response to a PUT request, for example, when two clients attempt to modify the same resource simultaneously, or when attempting to create a resource that already exists.

In version control systems, a 409 response might indicate an "edit conflict" where two users tried to update the same document at the same time.