a "handshake" of sorts, used in greeting or in congratulations. The hand is held in a first. In the longer version, one person taps the bottom of their fist against the top of the other person's fist, then the fists are to switch place and are tapped again, then they are tapped front-to-front.
In the shorter version, the closed fists are simply tapped front-to-front.
This front-to-front version became popular in a news clip of Michelle and Barack Obama. Fox News host E.D. Hill asked what to describe the maneuver, suggesting "terrorist fist jab."
I just stood there looking like a moron with my hand out, but he wouldn't look over and give me dap.
Definitions include: A circumcised male or circumcised penis. Well-known especially in Britain when boys compared their penises, and circumcision status, in school or college changing rooms. The uncircumcised are called cavaliers. The term refers humorously to the opposing sides in the English Civil War (1642-1651). In that war the Parliamentarians wore steel helmets and were nicknamed Roundheads. The Cavaliers were Royalists who had long flowing hair. The exposed glans penis of a circumcised male has some resemblance to such a helmet.