What is meant by the term "Conservation of Energy" in the nonfiction book, The New Way Things Work?

Energy is neither created nor destroyed. This is what meant by the term "Conservation of Energy" in The New Way Things Work. Energy can be harnessed, change forms or transferred from one object to another, but energy itself is constant. All actions require energy, except for nuclear reactions. Movement, heat and electromagnetic waves, including light, are forms of energy.