Refining (also called affining)'s the process of purification of a substance. The term's usually used of a natural resource that's almost in a usable form, but which's 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's broad, and may include more drastic transformations, such as the reduction of ore to metal (for which see Refining (metallurgy)).… (More on Refining)