The term "butt" has multiple meanings depending on its context.
1) In a general sense, it can refer to the rear end or backside of an object such as a chair, vehicle, or animal. For example, one might say that they are sitting in the butt of a car.
2) It is also used colloquially to mean "rump" or "hindquarters," referring specifically to the posterior region of the human body. This usage can be seen in phrases such as "sitting on your butt all day."
3) In some contexts, particularly in British English, it may refer to a cigarette, as in "I need a smoke - do you have any butts?"
4) Finally, the term is also used informally to mean "finish" or "end," as in "the party ended at midnight."