clear·ance / ˈkli(ə)rəns/ • n. 1. the action or process of removing or getting rid of something or of something's dispersing: there will be sunny intervals after clearance of any early mist. ∎  the removal of buildings, people, or trees from land so as to free it for alternative uses: slum clearance accelerated during the 1960s. ∎  (in soccer and other games) a kick or hit that sends the ball out of a defensive zone.2. official authorization for something to proceed or take place: a delay in obtaining diplomatic clearance to overfly Israel. ∎  (also security clearance) official permission for someone to have access to classified information. ∎  permission for an aircraft to take off or land at an airport. ∎  the clearing of a person or ship by customs. ∎  a certificate showing that such clearance has been granted. ∎  the process of clearing checks through a clearinghouse.3. clear space allowed for a thing to move past or under another: always give cyclists plenty of clearance.

clearance (renal clearance) (kleer-ăns) n. a quantitative measure of the rate at which waste products are removed from the blood by the kidneys. It is expressed in terms of the volume of blood that could be completely cleared of a particular substance in one minute.