British thermal unit
WordNet
noun
(1) A unit of heat equal to the amount of heat required to raise one pound of water one degree Fahrenheit at one atmosphere pressure; equivalent to 251.997 calories
WiktionaryText
Noun
British thermal unit (or BTU or Btu)
- The quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a particular temperature (there are several different precise definitions) and a pressure of one atmosphere. Symbol BTU or Btu.