Budget authority may be classified by period of availability (one year, multiple-year, or no year), by nature of the authority (current or permanent), by the manner of determining the amount available (definite or indefinite), or as gross (without reduction of offsetting collections) and net (with reductions of offsetting collections).
Net is one of the ways in which it's possible to classify budget authority.
Budget authority can't be classified by any means other than availability.