A limb is an arm or leg of a person or animal. Your four limbs help you move through the world: you use your arms to carry things, throw a ball, or give someone a hug, and you use your legs to run, jump, or climb stairs. Animals have limbs too. A dog has four limbs, all legs. A chimpanzee, like a human, has arms and legs that work differently from each other.

The word also refers to a large branch growing from a tree's trunk. When you climb a tree, you might sit on a sturdy limb. Tree limbs can be as thick as your leg or as wide as your whole body. They spread out from the trunk to hold up the tree's leaves and catch sunlight.

When someone goes out on a limb, they're taking a risk by supporting an unpopular idea or making a bold prediction. Imagine climbing out onto a thin tree branch: the farther you go, the more you're trusting it to hold you. Similarly, when you go out on a limb by defending a friend everyone else is criticizing, you're putting yourself in a vulnerable position because you believe it's the right thing to do.