I know this fist-bump gesture, but have never heard it called dap. Have you?

He [Barak Obama] gave some dap.

It was a split-second move, but it spoke volumes Moments before he addressed the Minnesota crowd last week, declaring victory in the race to be the Democratic presidential nominee, wife Michelle hit him with some dap—a quick movement in which two opposing fists touch lightly. … the gesture seemed to say, "Go ahead and knock 'em out the box."

Quick history lesson: The greeting evolved out of the black community (some say it stands for dignity and pride) and really was just a quick movement to say "hello." It's an offshoot of a soulful handshake folks in my parents' day used to do, and it has evolved over the years and has found its way into mainstream culture.
– Chicago Tribune, June 9, 2008

Never heard "dap". I thought it was called shake 'n' bake.

It is my understanding that those who are hip an cool know what "dap" means. This clarifies why I was unaware of the term.

Wikipedia says the dap greeting "has existed in the African-American community for centuries" but gives no references.

James E. Westheider, in Fighting on Two Fronts: African Americans and the Vietnam War (New York: New York University Press, 1997), says the dap was a ritualized handshake blacks used to greet each other in the Vietnam Warand that dap originated from dep, a Vietnamese word meaning "beautiful." Last paragraph, page 88.