Charcoal is the black substance left over when wood is heated in the absence of oxygen. You can cook with charcoal by burning it in your backyard grill.
Charcoal is used in many ways, but its most important use has probably been by blacksmiths and other metal workers, who historically used extremely hot charcoal fires to heat metal. Charcoal is also used to make explosive blasting powders and common water filters. One theory of the word's origin combines the obsolete verb charren, "to turn," and cole, "coal" — in other words, "to turn to coal."