Flammable means able to catch fire and burn easily. Gasoline is flammable, which is why gas stations post “No Smoking” signs. Paper, wood, and many fabrics are flammable too. When you see a flammable warning label on a product, it means you need to keep it away from flames, sparks, or high heat.

Scientists and safety experts prefer using flammable over inflammable (which means exactly the same thing) because inflammable confuses people. The prefix “in-” usually means “not,” so many people mistakenly think inflammable means “not able to burn” when it actually means the opposite. To avoid dangerous misunderstandings, warning labels now use flammable instead.

The opposite of flammable is nonflammable. Materials like steel, concrete, and glass are nonflammable because they won't catch fire under normal conditions. Understanding which materials are flammable helps keep people safe around campfires, candles, stoves, and anywhere else fire might be present.