What is Flammable Liquid?

Legal Definition
Generally, a flammable liquid is a combustible liquid that can easily catch fire. However, it is not the liquid itself that burns, but the vapor cloud above the liquid that will burn if the vapor's concentration in air is between the lower flammable limit (LFL) and upper flammable limit (UFL) of the liquid.
-- Wikipedia
Legal Definition
Liquid that has a flash point of 37.8c. This happens when the pressure is less than 60psi. The mix required for a flash point is 99% of the volume and is not flammable. Refer to combustible liquid.