The amount of energy it takes to raise the temperature of 1kg of a material by 1 degree kelvin is called specific heat. The unit for measuring specific heat is (J/kg*K)
Iron has a specific heat of 450 (J/kg*K)
Water has a specific heat of 4,180 (J/kg*K)
Waters relatively high specific heat means that it takes much more energy to heat water than to heat iron.
On a hot summer day at the lake, the air seems very warm but the water remains cool and refreshing. The reason the water is still cool is due to the relatively high specific heat of water. The lake hasn't absorbed enough energy to raise the temperature of the water to the same temperature as the air. The specific heat of water is much higher than the specific heat of air.