Refining (also perhaps called by the mathematical term
affining) is the process of
purification of a (1)
substance or a (2)
form. The term is usually used of a
natural resource that is 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 will 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
Refining (metallurgy)).