To rap is to hit something, talk, or bust into rhymes like the Fat Boys in the rap song “Human Beat Box” (1984). That’s some old school Brooklyn rap, but you can rap to any beat you want. Hit it!
A rap is a knock or blow, like if you rap somebody upside the head as a gentle reminder to pay attention. The word rap also means, "reputation,” like if you get a bad rap at school for sleeping in class. It’s also "to talk at great length." And there’s the musical rap, the “genre that includes talking rhythmically over a beat.” This meaning comes from African American slang for, basically, "talking.”