n. An intestinal parasitic worm, Ascaris lumbricoides, several inches long, infesting the human intestine: distinguished from the similar but much smaller pinworms or threadworms, and from the larger and more formidable flatworms, jointworms, or tapes.n. Hence Any member of the class Nematelmintha; a nematoid worm: distinguished from cestoid and trematoid worms, or tapeworms and flukes.