Answer
The minimum temperature needed for self-sustained combustion in absence of a spark or flame, at which the vapours from a volatile liquid will ignite spontaneously.
Explanation: autoignition temperature
The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion.