Source:
http://en.wikipedia.org/wiki/Security_clearance
A security
clearance is a status granted to individuals allowing
them access to classified
information, i.e., state secrets, or to restricted areas after
completion of a thorough background
check. The term "security clearance" is also sometimes used
in private organizations that have a formal process to vet employees for access to sensitive
information. A clearance by itself is normally not sufficient to
gain access; the organization must determine that the cleared
individual needs to know the
information. No one is supposed to be granted access to classified
information solely because of rank, position, or a security
clearance.