Flash point is the temperature at which a combustible or flammable substance will burn if exposed to a spark. The flash point enters into safety during shipping and storage, because a low flash-point material in a fire can make the fire much worse. That is why there are often hazardous material charges or restrictions on shipping low flash point materials. When the material is mixed with other stuff, like soap for instance -- the flash point of that one ingredient does not apply to the whole.
Flash point can be used as a rough measure of how volatile a flammable/combustible substance is. Bear in mind that not all volatile substances are flammable or combustible, so flash point isn't an absolute measure of volatility. For example, water is not flammable or combustible, but it is volatile (evaporates easily). As another example, common soaping oils are combustible, but they do not evaporate easily at all.
Many people use the flash point as the temperature at or below which they can "safely" add fragrance to soap. I don't pay any attention to that -- the flash point temp in this context is pretty much meaningless. When mixed into the soap, the fragrance won't burn for one thing. For another, one shouldn't be handling any fragrance or other flammable substance when close to open flame. And finally, fragrance, even if it is below its flash point, is still going to evaporate -- the warmer the soap, the faster the evaporation. My goal, whatever the fragrance, is to add it at the coolest temperature I can manage.
