The height above the ground or water of the base of the lowest
layer of cloud below 6000 meters (20,000 feet) covering more
than half the sky. United Kingdom  In relation to an aerodrome,
the vertical distance from the elevation of the aerodrome to the
lowest part of any cloud visible from the aerodrome which is
sufficient to obscure more than one half of the sky so visible.
A ceiling or cloud ceiling means the height above the Earth's
surface of the lowest layer of clouds or obscuring phenomena
that is reported as broken, overcast, or obscuration, and not
classified as thin or partial. A ceiling listed as "unlimited"
means that the sky is clear or is free of any substantial cloud
cover. Ceiling is reported as part of the METAR (METeorological
Aviation Report) used for flight planning by pilots worldwide.
See also  - Visual flight rules (VFR) - UK Air Navigation Order
- Section 1.1 14 CFR Part 1 - Definitions - Federal Air
Regulations