The documents are only available to people with 'security clearance' [=special permission given only to people who are approved to know or see secret things] from the government.
The car has a 'road/ground clearance' of seven inches. [=the bottom of the car is seven inches above the road/ground]
You'll have to get 'clearance' [='approval'] from management to go ahead with the project.
(..) - I need to meet you. If you need to confirm who I am, you can talk to my boss at the Circus, Peter Guillam. But only Guillam, no one else. You got clearance for that? Well, I'm not bloody chaining it up outside. Mind you, no better off in here with this bunch of bloody cut-throats. (..)2011 Tinker Tailor Soldier Spy