Plain English Meaning
An OpSpec is the FAA-approved rulebook for one specific operator. It spells out exactly what that operator is allowed to do, what equipment they can use, and any conditions they must follow.
Full Definition
An operations specification (OpSpec) is a formal document issued by the FAA to a certificate holder (such as an air carrier or commercial operator) that authorizes and defines the specific operations that operator may conduct. It lists the approvals, limitations, and conditions under which the operator can fly — including authorized aircraft, routes, airports, navigation systems, instrument approach types, and special procedures. OpSpecs are tailored to each operator and form part of the legal framework governing how that operator may use its certificate.