To fail to remember something. I often forget where I put my keys.
To inadvertently neglect to do something. She forgot to lock the door before leaving.
To put out of one's mind; cease to think of or consider. He tried to forget the embarrassing incident.
(imperative) Used to tell someone not to worry about something or to disregard what has been said. "Forget it," he said, "I'll deal with the problem myself."