See rights clearance.
Clearance is a
[f]ormal security determination by an authorized adjudicative office that an individual is authorized access, on a need to know basis, to a specific level of collateral classified information (TOP SECRET, SECRET, CONFIDENTIAL).
[f]ormal certification of authorization to have access to classified information other than that protected in a special access program (including SCI). Clearances are of three types: confidential, secret, and top secret. A top secret clearance permits access to top secret, secret, and confidential material; a secret clearance, to secret and confidential material; and a confidential clearance, to confidential material.