Refining (also called affining) is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that's almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it'll burn poorly and quickly clog an engine with residues and by-products. The term is broad, and may include more drastic transformations, such as the reduction of ore to metal (for which see R… (More on Refining)