Fireproof means unable to be damaged or destroyed by fire. A fireproof safe protects important documents even if a house burns down around it. Fireproof clothing helps protect firefighters in burning buildings by greatly reducing the chance that their gear will catch fire.

Fireproof materials are designed to resist fire extremely well: they are very hard to burn and can stay strong at high temperatures. Asbestos was once used widely because it is naturally very fire resistant, though we now know it causes serious health problems. Modern fireproof materials include special ceramics, treated fabrics, and metal alloys that stay strong even at extreme temperatures.

The word also appears in the related term fire-resistant, which means something that slows fire down but might eventually burn. A fire-resistant door gives people extra minutes to escape, while a fireproof vault is designed to protect its contents for a very long time in a fire. Building codes often require fireproof or fire-resistant materials between apartments so a fire in one unit doesn't quickly spread to others.

Sometimes people use fireproof more loosely, like calling a plan fireproof when they mean it can't fail. But the literal meaning refers specifically to materials that fire cannot easily harm.