butt

Your butt is your bottom, your bum, the part of your body that you sit on.

Example: The exercise works your legs, butt, and back.

When someone says, get your butt over/back/out of here, they mean move yourself.

Example: Get your butt over here. = come here

If someone or something is a pain in the butt, they are unpleasant or annoying.

Example: Stop that! You're such a pain in the butt.

If you work/run/study/play your butt off, you do so very hard.

Example: We played our butts off in the game today, and we still lost.

The butt of something is its end.

Example: He threw his cigarette butt on the ground.