Rat , common name for any large member of a family of rodents, with dull-colored, coarse fur; long tails; large ears; and a pointed snout. Rats have extremely powerful teeth, with which they often gnaw through wooden planks to get at stores of food, and they have even been known to bite holes in lead pipes. They are usually nocturnal and live in human habitations, in forests, in deserts, and on seagoing ships. They are extremely prolific, breeding 1 to 13 times a year and producing 1 to 22 young in a litter. Most species of rats are herbivorous, but some are omnivorous .