LET/ALLOWofficial permission for someone to see secret documents etc, or to enter a building, after a strict checking process 〔经过严格安全审查后〕对参加机密工作的批准；出入某建筑物的许可
Examples from the Corpus
security clearance• Another son, Ron, is a Lockheed employee with a security clearance.• In preparation for his job at Commerce, Huang received an interim security clearance while he was still working at Lippo.• A visitor without security clearance must be signed for by the sponsor and accompanied at all times.