What is Activated Carbon?

Legal Definition
Activated carbon, also called activated charcoal, is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. 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 3,000 m2 (32,000 sq ft), 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 is sometimes utilized as biochar. Those derived from coal and coke are referred as activated coal and activated coke respectively.
-- Wikipedia
Legal Definition
A carbon used in catalytic coverters and waste treatment. It removes toxicity to the environment. One gram neutralizes 1,000 sq meteres. Refer to molecular sieve.