A parasitic nematoid worm, especially the roundworm, Ascaris lumbricoides, often occurring in the human intestine, and allied species found in domestic animals; also commonly applied to the pinworm (Oxyuris), often troublesome to children and aged persons.

A type of roundworm.

a worm that lives in the small intestine

large intestinal roundworm that infects foals and young horses. May retard growth or block intestines.