A ceiling is the upper interior surface of a room, the part you see when you look straight up from inside a building. While floors bear weight and walls provide structure, ceilings complete the enclosure of indoor space. Most ceilings are flat and painted white, but some feature decorative elements like molding, wooden beams, or even elaborate artwork, like the famous painted ceiling of the Sistine Chapel in Rome.

The word also means an upper limit, particularly in contexts involving numbers or achievements. In aviation, a plane's ceiling is the maximum altitude it can reach. Government agencies sometimes set a debt ceiling, which limits how much money can be borrowed. When someone talks about breaking through a glass ceiling, they mean overcoming invisible barriers that prevent certain people from advancing in their careers, regardless of their abilities.

You might hear someone say they're “hitting a ceiling” in their progress at something, meaning they've reached as far as they can go without changing their approach. A basketball player might hit a ceiling in how high they can jump, or a student might hit a ceiling in math until they learn new techniques. Understanding your ceilings helps you figure out what you need to do differently to keep improving.