A rat is a medium-sized rodent from the genus Rattus, known for its long, hairless tail, sharp teeth, and adaptability. Common species include the brown rat (Rattus norvegicus) and the black rat (Rattus rattus). Rats are highly intelligent, social, and nocturnal animals that thrive in both wild and urban environments. They are omnivores, reproduce quickly, and are excellent climbers and swimmers. While often considered pests due to their role in spreading disease and damaging property, they also play important roles in ecosystems and scientific research.