A billy goat is a male goat. The word billy is an informal, friendly way to specify that you're talking about a male rather than a female goat (which is called a nanny goat). You'll often hear this term on farms or in stories like “The Three Billy Goats Gruff,” where three male goats must outwit a troll living under a bridge.

Billy goats are known for being tough, sturdy, and sometimes stubborn animals. They often have beards and can grow impressive curved horns. Male goats also have a strong, distinctive smell, especially during mating season.

People sometimes use billy goat playfully to describe someone with a scraggly beard, or they might say someone is “as sure-footed as a billy goat” when talking about someone who can climb or balance on difficult terrain, since goats are famous for scrambling up steep, rocky hillsides that would be dangerous for most other animals.