Rats are various medium-sized, long-tailed rodents.
Species of rats are all found in Rodentia, and are present throughout the order. Typical rats are found in the genus Rattus.
Rats are typically distinguished from mice by their size. Generally, when someone discovers a large muroid rodent, its common name includes the term rat, while if it is smaller, the name includes the term mouse. Common terms rat and mouse are not taxonomically specific. Scientifically, the term rat is not confined to members of the Rattus for example, the pack rat.