the number of heat needed to enhance the temperature of just one lb of liquid from 60° to 61°F at a continuing force 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.

the amount of temperature required to improve the heat of 1 lb of liquid one level Fahrenheit at a certain heat (there are lots of different exact meanings) and a pressure of one atmosphere.

a unit of heat equal to the total amount of temperature needed to raise one pound of water one level Fahrenheit at one environment force; equivalent to 251.997 calories

## How would you define British thermal unit?