- Containing information whose unauthorized disclosure would pose the gravest threat to national security: authorized for access to top-secret reports.
- Of or relating to top-secret information: top-secret clearance.
- Accessible or known to authorized personnel only: a top-secret reconnaissance mission.
- Having the highest secrecy classification.
- (military) Information classified at the highest level of sensitivity by a government, based on an assessment that it would cause exceptionally grave damage to national security if disclosed.
- NSA's report on the Liberty incident was originally classified top secret.
- A level of security clearance needed to access such information.
- (figuratively) Pertaining to any especially sensitive closed-room activities.
- Steve Jobs set up a top secret team to design the Macintosh.