A callus is a patch of thick, hardened skin that forms where your body experiences repeated rubbing or pressure. Guitar players develop calluses on their fingertips from pressing steel strings hour after hour. Gymnasts get them on their palms from gripping bars. Runners might get calluses on their feet where shoes rub against the same spot with every stride.

Your skin builds these tough patches to protect itself. The first few times you rake leaves or use a shovel, your hands might hurt or even blister. But if you keep doing that work, your skin thickens in those exact spots, creating natural armor. That's a callus. It's your body adapting to the work you're asking it to do.

Calluses don't hurt, unlike blisters, which are filled with fluid and tender to the touch. A callus is just tougher skin. Many musicians and craftspeople wear their calluses with pride because they show dedication and hours of practice. When a cellist's fingertips have thick calluses, you know they've put in serious work mastering their instrument.

The word callous (spelled differently) means emotionally hardened or uncaring, like someone who doesn't seem affected by others' feelings. While the spelling and meaning differ, there's a connection: both suggest something that has become tough and less sensitive.