Whipworm: A nematode (roundworm), also called Trichuris trichiura, that is the third most common roundworm in humans. The whipworm is found worldwide, and whipworm infections are most frequent among children and in areas with tropical weather and poor sanitation practices. Infection with whipworm most often occurs without symptoms. Heavy infections, especially in small children, can cause gastrointestinal problems (such as abdominal pain, diarrhea, and rectal prolapse) and possibly growth retardation. Treatment involves use of the drugs albendazole or mebendazole.