clear·ance 
(klîrəns)
(klîrəns)n.
1. The act or process of clearing.
2. A space cleared; a clearing.
3.
a. The amount of space or distance by which a moving object clears something.
b. The height or width of a passage: an underpass with a 13-foot clearance.
4. An intervening space or distance allowing free play, as between machine parts.
5. Permission for an aircraft, ship, or other vehicle to proceed, as after an inspection of equipment or cargo or during certain traffic conditions.
6. Official certification of blamelessness, trustworthiness, or suitability.
7. A sale, generally at reduced prices, to dispose of old merchandise.
8. The passage of checks and other bills of exchange through a clearing-house.
9.
a. The removal by the kidneys of a substance from blood plasma.
b. Renal clearance.