Temperature is a measure of the level of motion or agitation of molecules and atoms in a substance. In other words, it is a measure of the intensity of heat. Thermometers, used to determine the temperature, do so in terms of one of two common scales of degrees: Fahrenheit (F), on which water freezes at 32° and boils at 212°, and Celsius (C), on which water freezes at 0° and boils at 100°.

The difference between heat and temperature is important. If you have one gallon of water at 50°F and 10 gallons of water at 50°F, both are at the same temperature; however, the 10 gallons contain 10 times the amount of heat (the number of Btu).