the.com/flash point

means The lowest temperature at which a substance gives off enough vapor to flash into flame when a spark hits it — and by extension, the moment any tense situation suddenly erupts.

from Born in 19th-century chemistry and materials testing, where chemists needed a precise, measurable number for how flammable an oil or fuel really was — literally the 'point' at which it would 'flash' alight. The word later jumped from laboratories into politics and conflict reporting, where a 'flashpoint' became any place or moment where tension ignites into violence — the metaphor keeping its combustion intact.