What characteristic describes a substance that can easily catch fire?

A substance that can easily catch fire is described as flammable. This term specifically refers to materials that ignite easily and burn rapidly upon exposure to an open flame or sparks. Flammable substances generally have low flash points, meaning they can produce vapors that ignite at relatively low temperatures, making them hazardous in environments where fire or heat sources are present.

While combustible materials can also catch fire, they typically require higher temperatures to do so and burn more slowly than highly flammable materials. The term explosive refers to substances that undergo a rapid chemical reaction producing gas and heat, leading to an explosion, rather than simply catching fire. Non-flammable indicates an inability to catch fire at typical temperatures. Therefore, "flammable" is the most accurate descriptor for substances that ignite easily and poses significant fire risks.