A shield is a piece of protective equipment held in front of the body to block attacks. For thousands of years, warriors carried shields into battle: round wooden shields, tall rectangular Roman shields, or small medieval bucklers strapped to the forearm. A shield turns aside arrows, deflects sword strikes, and absorbs the impact of blows that might otherwise injure or kill.

The word also means to protect someone or something from harm or danger. A parent might shield their child from scary news, or a lawyer might shield a client from unfair accusations. Trees can shield hikers from rain, and sunscreen shields your skin from harmful ultraviolet rays.

In science fiction and video games, you'll often encounter energy shields or force fields that work like invisible barriers protecting spaceships or buildings. These imaginary shields work on the same basic principle as ancient wooden ones: they stand between something valuable and whatever threatens it.

When you shield something, you place yourself or something else between it and danger to keep it safe. That's why we call protective barriers heat shields on spacecraft or blast shields in laboratories.