106. Which of the following terms defines the minimum temperature required to ignite gas or vapor without a spark or flame being present?

Autoignition temperature is the minimum temperature at which a substance ignites spontaneously without an external ignition source. This definition aligns with the question's requirement for ignition without a spark or flame, differentiating it from flash point, fire point, and lower explosive limit, which all involve an external ignition source or represent a concentration rather than a temperature.