A situation in which things are confused or not organized properly, leading to mistakes or misunderstandings. There was a mix-up at the airport, and my luggage was sent to the wrong destination.
An error or mistake resulting from confusion or miscommunication. Due to a mix-up in the schedule, the meeting was canceled without notice.
Informal: a fight, skirmish, or minor physical altercation. He ended up in a mix-up outside the bar but no one was seriously hurt.