A gesture of celebration or greeting performed by two or more people by bumping their fists together. Sometimes incorrectly referred to as a 'fist bump.' The term Fo' Knucks derives from a shortening of the words "four knuckles" -- i.e., the number of knuckles making contact on each fist.
If requesting another round of Fo' Knucks, an individual may ask for "Fo' Mo'."
"Michelle Obama gave Barack Fo' Knucks when he secured the Democratic nomination."
"Hey, Ben, I slept with your sister." "Oh, yeah? Fo' Knucks!"