Specific heat is a measurement used in thermodynamics and calorimetry that states the amount of heat energy necessary to increase the temperature of an object by some unit of temperature. While different scales of measurement are sometimes used, typically specific heat specifically refers to the amount of heat energy required to raise a single gram of some substance by one degree Celsius or by one Kelvin (one Kelvin is the same as one degree Celsius). It follows that if twice as much heat is added to a substance, its temperature should increase by twice as much. Specific heat is usually expressed in joules, the unit typically used in chemistry and physics to describe energy.

Heat energy and temperature are two different concepts; understanding the difference is important to understanding the concept of specific heat. Temperature is merely a relative measurement used to describe how "hot" or "cold" an object or substance is. Heat energy, on the other hand, is a quantity in thermodynamics that describes the amount of change that a system can cause on the environment. Heat energy causes the molecules in a substance to move around more rapidly; this increase in kinetic energy leads to an increase in temperature. The transfer of heat energy leads to changes in temperature.

There are two different values involving specific heat that are often confused: specific heat capacity and thermal mass, which is also known as heat capacity. The first is the amount of heat energy required to increase a mass of a substance by some unit of temperature. The second, on the other hand, is the capacity of an object or substance to store or contain heat, and is almost always measured in joules per Kelvin or joules per degree Celsius. Similar units and names often lead chemistry students to some level of confusion.

Water, which can be found in massive amounts all over the world, has a very high specific heat. Because of the molecular structure of water, a great deal of heat energy is needed to increase its temperature by even a small amount. This property of water is essential to life on earth, as the temperature of water has a significant stabilizing effect on the global climate. In particularly cold weather, the Earth's water supply cools down slowly and release a significant amount of heat into the environment, which keeps the global temperature reasonably stable. Conversely, in very warm weather, it takes a great deal of heat to significantly increase the temperature of the Earth's water, which also prevents significant climate change.