A flash point is the temperature at which a liquid gives off enough vapor to ignite if exposed to a spark or flame. Gasoline has a very low flash point (around negative 45 degrees Fahrenheit), which is why it's so dangerous: even on a cold day, gasoline vapors can catch fire instantly. Water, by contrast, doesn't have a flash point in everyday conditions because it doesn't produce flammable vapors.

Understanding flash points matters for safety. Firefighters need to know the flash points of different chemicals to handle them properly. Factory workers store flammable liquids carefully based on their flash points. If you've ever seen a warning label that says “Keep away from heat or flame,” it's there because that substance has a relatively low flash point.

The term also means a point of crisis where conflict suddenly erupts into violence or confrontation. When tensions between two groups have been building for a long time, people might say the situation has reached a flash point. A heated argument between friends might reach a flash point where someone storms off. Like the scientific meaning, this usage suggests something volatile that can ignite quickly: the conditions are right for an explosion, whether literal or figurative.