Plain English Meaning
A way of measuring temperature where freezing water is 0 and boiling water is 100. It is the temperature scale pilots use almost everywhere in aviation.
Full Definition
A temperature scale on which water freezes at 0 degrees and boils at 100 degrees at standard sea-level pressure. In aviation, Celsius is the standard unit used for reporting outside air temperature, weather observations, forecasts, and performance calculations.
Context Anchor
Seen in aircraft performance charts, weather information, and standard atmosphere discussions.
Derivation
Named after Anders Celsius, the Swedish astronomer who proposed the 0-to-100 scale in 1742. Knowing the name is just a helps avoid the assumption that 'Celsius' refers to some technical property of the itself.