Things that curl bend in a spiral or circular shape. When you curl your hair, you use heat to make it wavy and coiled.
You can curl a lock of hair around your finger, or curl your body up in a chair. You can also call the shape you're forming a curl. A completely different way to curl is to play the Olympic sport known as curling, which is a little like shuffleboard on ice. The sport comes from Scotland, and the word probably comes from the Middle Dutch krul, "curly."