Your thumb is the short, thick finger on the side of your hand that can swing across your palm to touch your other fingers. This special ability is called an opposable thumb.

Try picking up a pencil without using your thumb. It's nearly impossible! Your thumb works with your fingers to create a powerful grip. When you hold a baseball bat, turn a doorknob, button your shirt, or tie your shoes, your thumb does most of the work. Even typing on a phone often depends on your thumbs.

The phrase rule of thumb means a simple, practical guideline rather than an exact rule. If someone says, “as a rule of thumb, bring a jacket when it's below 60 degrees,” they're offering useful advice, not a strict law. When you're all thumbs, you're being clumsy or awkward with your hands, like when you keep dropping things or can't work the controls on a new video game.

People sometimes thumb through a book, flipping pages quickly with their thumb to find something. And if you give someone a thumbs up, you're showing approval or saying everything's good to go.