Dogs are domesticated mammals and are often referred to as man's best friend due to their loyalty and companionship. They belong to the family Canidae and have been bred for various purposes, including herding, hunting, and providing assistance to humans. With a wide range of breeds, dogs vary greatly in size, shape, and temperament. They are known for their intelligence and ability to learn commands, making them popular as pets and working animals. Dogs also play important roles in therapy, search and rescue, and law enforcement, showcasing their versatility and value to society.