Activated carbon, also called activated charcoal or activated coal, is a general term which covers carbon material mostly derived from charcoal. For all three variations of the name, "activated" is sometimes substituted with "active". By any name, it is a material with an exceptionally high surface area. Just one gram of activated carbon has the surface area of approximately two tennis courts, typically determined by nitrogen gas adsorption, and includes a large amount of microporosity.