What are clearances?

Some articles on clearances, clearance:

Types and Documentation of Credentials - Security Clearances
... have access to such information are issued security clearances, which can be tracked and verified to ensure that no unauthorized persons gain access to protected information ... Security clearances are among the most carefully guarded credentials ... The most elaborate security-clearance systems are found in the world's military organizations ...
Macaulay Family Of Lewis - Hebridean Feuds - 19th Century: Evictions, Clearances, and Emigration
... Although the Lewis evictions were not on the same scale as those elsewhere in the Highlands, the mass evictions, and deserted villages within the parish of Uig, were a testament to the Highland Clearances ... In 1793, Francis Humberston Mackenzie advertised the whole parish as a sheep farm later in 1796 he issued 133 summonses of removal to its tenants ...
Ben Bhraggie - George Leveson-Gower
... The Sutherland clearances were not by any means the only clearances - this period saw similar occurrences throughout Scotland, not just in the Highlands but in many rural lowland areas as well ... However the Sutherland clearances are among the most notorious ...
Abradable Coating
... compressor and turbine sections where a minimal clearance is needed between the blade tips and the casing ... In typical turbo machinery, the clearance between blade tips and the casing must account for thermal expansion as well as changes in concentricity due to shock loading events ... tip to casing contact, conservatively large clearances must be employed ...
Strathnaver - Clearances
... Strathnaver saw some of the most notorious forced evictions of the Highland clearances carried out by the Duke and Duchess of Sutherland ...