147. What is the lowest temperature at which a liquid gives off sufficient vapors to form a flammable mixture with air in the presence of an ignition source?

The flash point is the lowest temperature at which a liquid produces sufficient vapor to form an ignitable mixture with air when an ignition source is applied. This definition directly addresses the question's parameters, distinguishing it from the Reid vapor index (a pressure measurement), the flammable range (a concentration range), and the autoignition temperature (ignition without an external source).