a unit of heat equal to about 252 calories; quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit: abbrev. Btu
See British thermal unit in American Heritage Dictionary 4
noun Abbr. BTU or Btu
The quantity of heat required to raise the temperature of one pound of water from 60° to 61°F at a constant pressure of one atmosphere.
The quantity of heat equal to 1/180 of the heat required to raise the temperature of one pound of water from 32° to 212°F at a constant pressure of one atmosphere.