The story
So called because it can be visualised as the set of handshakes if n couples go to a party and each person shakes hands with every person except his or her partner.
Etymology from Wiktionary, CC BY-SA 4.0.
cocktail party graph
Today it means: A graph consisting of two rows of paired nodes in which all nodes except the paired ones are connected with straight lines; it is the complement of the ladder rung graph, and the dual graph of the hypercube. Full definition →