a class of animals to which humans, cows, lions, etc. belong, having warm blood, fur or hair and producing live offspring
What is "mammal"?
Mammal is a warm-blooded animal that belongs to the class Mammalia. All mammals have certain defining characteristics, including the presence of hair or fur, the ability to produce milk to feed their young and three middle ear bones. Mammals are also capable of regulating their body temperature internally, which makes them well-adapted to live in a wide range of environments. There are around 5,500 species of mammals, including many familiar animals such as humans, dogs, cats, elephants, whales, and bats. Mammals play important roles in ecosystems around the world and are often key indicators of environmental health. They are also a major source of food, clothing, and other resources for humans.