Yours, Etc.: Origins and Uses of 8 Sign-Offs
originally U.S. basketball slang, 1980 as a noun, 1981 as a verb, though the greeting itself seems to be older (e.g. Dick Shawn in "The Producers," 1968). In reference to the five fingers of the hand.
A way of greeting or congratulating by slapping raised palms together •Chiefly used by and adopted from athletes, who themselves adopted the style from black colleagues: handshaking, even a few high-fives from the younger alumsverb phrase
GIVE someone FIVE: Roberts is not the kind to engage in trash-talking or high-fiving