The low five is a hand gesture when two people slap palms together. One party extends an open palm, face upward at about waist level, the other party strikes the palm in a downward swing with their open palm. It's sometimes known as "slapping five", "give me five", or "giving/slapping skin". Archaic terms for it include "slip-slapping", "slapping the plank" and "soul shake".
The gesture is an antecedent of the high five which appeared in the 1970s.