The definition of a bull is, simply put, a male cow. Unlike cows, bulls often have horns. Bulls are often more aggressive than cows, and can often fly into a rage-like state in which they will use their horns to charge various things. Indeed, bulls have become quite famous for their rage through bull fights, which are common in Spain. During a bull fight, a picador will slice and poke at a bull with a sword to irritate it. Then, a matador will use a red cloth to enrage the bull, and then attempt to kill the bull with a sword. However, bulls are very dangerous when thus enraged and many matadors have suffered at the sharp horns of the bull.
Cows and bulls are mammals, in the same family as cats, dogs, monkeys, whales, dolphins, and humans. Bulls are not used as often on farms as cows are because they do not produce milk, and also because of their temperamental nature. The term bull usually refers to the adult male cow.