Ceiling (cloud)

In aviation, ceiling is a measurement of the height of the base of the lowest clouds (not to be confused with cloud base which has a specific definition) that cover more than half of the sky (more than 4 oktas) relative to the ground. Ceiling is not specifically reported as part of the METAR (METeorological Aviation Report) used for flight planning by pilots worldwide, but can be deduced from the lowest height with broken (BKN) or overcast (OVC) reported.^[1] A ceiling listed as "unlimited" means either that the sky is mostly free of cloud cover, or that the clouds are high enough not to impede visual flight rules (VFR) operation.