The singular posterior opening of the intestinal and urinary tracts of birds, reptiles, amphibians, marsupials and monotremes.

A cloaca ( kloh-AY-kə), pl.: cloacae ( kloh-AY-see or kloh-AY-kee), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilaginous fish and a few mammals (monotremes, afrosoricids, and marsupial moles, etc.) have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have separate orifices for evacuation and reproduction...