Past events have already happened — if it happened an Ice Age ago, a century ago, or even a minute ago, it's in the past.
They say the past is history and it's true. If you have ever been accused of "living in the past," you cling to what was instead of reveling in what is. If you hear that a person or a rare object in an antique store "has a past," get ready for a colorful story. As an adjective, past describes what is no longer current, like the past president of a club or past fashion craze — it's over: its time has passed.