1) An attractive girl's butt;
2) Picture of an attractrive girl showing her ass, either nude or partially nude, as opposed to boob bait;
3) Example of jailbait that is especiallyattractive because of her well-formed behind.
A state of being unable to remember seemingly simple things such as keeping appointments and returning phone calls.
While occasionally a natural condition for some people, it is most often a temporary state triggered by excess stress and/or a lack of sleep. It should not be considered an accurate indicator of a person's intelligence.
I didn't mean to stand you up at the coffee shoplast night. I got a bit moonbrained and completely forgot we had plans.