It means to make someone happy when there Sad. Mostly used when the persons name is Caboose. A term I use very often next time use the word Caboost.
When feeling down and someone makes you feel better the other person just gave you a caboost.
another word for your butt, your ass, your hind-quarters,or that your simply last : ]
little timmy today your the caboost!
simply meaning your the ass of the line ......