Cloud Height Definitions MET
There are three concepts associated with vertical distances with clouds: cloud base, cloud ceiling, and cloud top.
Cloud base and cloud top have a "natural" meaning - cloud base is the bottom of the cloud irrespective of coverage measured as a height (above the ground or water) and cloud top is the top of the cloud measured as an altitude or in flight levels.
Cloud ceiling is the tricky one - firstly, think of the ceiling above you. That is the lowest part of whatever roof or floor is above you, and the same is true of the cloud ceiling - it is the lowest cloud covering at least half the sky below 20,000'. Intuitively, this makes sense - the ceiling above you wouldn't be much of a ceiling if more than half of it was exposed to sky. For practical purposes, broken (BKNBKN —METARMETAR —Meteorological Actual Report/TAFTAF —Terminal Aerodrome Forecast code for 5-7 oktas of cloud) and overcast (OVCOVC —METAR/TAFTAF —Terminal Aerodrome Forecast code for 8 oktas of cloud) clouds count as at least half - scattered and few do not.