A casement is a window that opens on hinges, like a door. Instead of sliding up and down, a casement window swings outward or inward, usually with a crank or handle to control it. You might spot casement windows in older houses, churches, or castles, where they often have small panes of glass held together by metal or wooden frames.

Casement windows were common in medieval buildings because they could be made weatherproof more easily than other designs. In Shakespeare's Romeo and Juliet, Juliet appears at a casement window when Romeo sees her and delivers his famous speech about her beauty.

Today, casement windows are still popular because they can catch breezes better than windows that only slide open partway. When you crank open a casement window, you're opening it completely to one side, creating a wide opening for fresh air to flow through.