A form of celebration when two people slap the opposing palms of one hand, or sometimes both, together with arms raised. There are many claimants for the origin but the only certainty is that it originated in American sport, possibly baseball or basketball, in the late 1970s. The phrase was included in the OED in 1980. It is associated with the 'low five', a similar form of celebration or greeting, which originated in black American culture in the 1940s. See also Low Five.