Celcius was a unit of measurement indicating temperature.

The Second Doctor was worried that a creature the Mercurial were afraid of might begin to move if they were well below zero degrees Celsius. At the time, the thermostat indicated three degrees. The Doctor discovered, in the end, that the creatures they feared were merely solar pylons. (PROSE: Mercury)

The Twelfth Doctor's sonic sunglasses gave him, while he was blind, such data as people's body temperature, given in degrees Celsius. (TV: Extremis, The Pyramid at the End of the World)

Community content is available under CC-BY-SA unless otherwise noted.