Activated carbon, also called activated charcoal, activated coal, or carbo activatus, is a form of carbon processed to be riddled with small, low-volume pores that increase the surface area available for adsorption or chemical reactions.[1] Activated is sometimes substituted with active.

Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2, as determined by gas adsorption. An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment often enhances adsorption properties.

Activated carbon is usually derived from charcoal and increasingly, high-porosity biochar.