Basically, energy refers not to gas, oil or electricity but to the capacity of a body or system to exert enough force to move something. This can involve one atom bumping into another, a person pushing a stalled car or two galaxies colliding. The amount of work accomplished depends on how much force is used and how far the object is moved. Scientists measure energy in units called joules after the 19th century English physicist, James Prescott Joule. In everyday terms, a joule is tough to describe.
Ergs are very, very small.
Ten million ergs equals one joule. As it turns out, all matter is a form of energy because all matter can do work. This includes everything from couch potatoes to real potatoes. It's just that you can't always see it. For example, stars radiate moving light and heat while invisible plasma gases continually sweep through space.