The word "macaca" is defined as "A genus of Old World monkeys including the rhesus monkey and other macaquas." A similar sounding word, "Makak", is defined as "A person of North African origin, derived from macaquas monkeys; ethnic slur."
During a campaign rally in Virginia, George Allen referred to one of his opponents volunteers as "macaca". S.R. Sidarth, the actual name of the volunteer, had introduced himself to Senator Allen only minutes before.
On last night's Daily Show, John Stewart and Rob Corddry lampoon the Senator's mistaken comment.