degree day

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A measure of heating or cooling, computed as the integral of a function of time that generally varies with temperature.
• noun A unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the base temperature, often 65F.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the day on which university degrees are conferred
• noun a unit used in estimating fuel requirements for heating a building