Specific heat is the amount of heat necessary to increase the temperature of a substance one degree Celsius. Different materials have different specific heats depending on what they are made of and how their atoms are arranged. Specific heat is measured in units of J/g * C.
For example, the specific heat of air is 1.01 J/g * C and the specific heat of water is 4.179 J/g *C. This means it takes almost four times as much heat to change the temperature of water than it does to change the temperature of air. Water maintains a constant temperature more easily than air does.