Meaning

originUS 1971, originally by black soldiers during the Vietnam war, associated with Black Power movement. Originally an elaborate handshake, later specifically a fistbump. Verb originally give dap. Presumably onomatopoeic, or influenced by tap, dab, etc. Alternatively, from earlier slang usage as abbreviation of dapper. Also explained as an acronym, such as “Dignity for Afro People” or “Dignity And…

Etymology from Wiktionary, CC BY-SA 3.0