1. To agree with something. Comes from the Military Saying "
Affirmative," which was said by soldiers
in the Heat of battle as "Fucking Affirmative" which was later shortened to "
Fucking A"
2. However over the years the meaning of this phrase has been changed and is now used to express something as good.
3. Also can be used to describe something bad.
4. Pretty much can be used for anything depending on the user