What is "energy carrier"

n. A substance or phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes (http://en.wikipedia.org/wiki/ISO%2013600).

An energy carrier is a substance (energy form) or sometimes a phenomenon (energy system) that contains energy that can be later converted to other forms such as mechanical work or heat or to operate chemical or physical processes. Such carriers include springs, electrical batteries, capacitors, pressurized air, dammed water, hydrogen, petroleum, coal, wood, and natural gas. An energy carrier does not produce energy; it simply contains energy imbued by another system.