Energy. Energy is a property associated with a material body. Energy is not a material substance. When bodies interact, the energy of one may increase at the expense of the other, and this is sometimes called a transfer of energy. This does not mean that we could intercept this energy in transit and bottle some of it. After the transfer one of the bodies may have higher energy than before, and we speak of it as having "stored energy". But that doesn't mean that the energy is "contained in it" in the same sense as water in a bucket.
Misuse example: "The Earth's auroras—the northern and southern lights—illustrate how energy from the sun travels to our planet." —Science News, 149, June 1, 1996. This sentence blurs understanding of the process by which energetic charged particles from the sun interact with the Earth's magnetic field and our atmosphere to cause auroras.
Whenever one hears people speaking of "energy fields", "psychic energy", and other expressions treating energy as a "thing" or "substance", you know they aren't talking physics, they are talking moonshine.
In certain quack theories of oriental medicine, such as qi gong (pronounced chee gung) something called qi is believed to circulate through the body on specific, mappable pathways called meridians. This idea pervades the contrived explanations/rationalizations of acupuncture, and the qi is generally translated into English as energy. No one has ever found this so-called "energy", nor confirmed the uniqueness of its meridian pathways, nor verified, through proper double-blind tests, that any therapy or treatment based on the theory actually works. The proponents of qi can't say whether it is a fluid, gas, charge, current, or something else, and their theory requires that it doesn't obey any of the physics of known carriers of energy. But, as soon as we hear someone talking about it as if it were a thing we know they are not talking science, but quackery.
The statement "Energy is a property of a body" needs clarification. As with many things in physics, the size of the energy depends on the coordinate system. A body moving with speed V in one coordinate system has kinetic energy ½mV2. The same body has zero kinetic energy in a coordinate system moving along with it at speed V. Since no inertial coordinate system can be considered "special" or "absolute", we shouldn't say "The kinetic energy of the body is ..." but should say "The kinetic energy of the body moving in this reference frame is ..."
Energy (take two). Elementary textbooks often say "there are many forms of energy, kinetic, potential, thermal, nuclear, etc. They can be converted from one form to another." Let's try to put more sturcture to this. There are really only two functional categories of energy. The energy associated with particles or systems can be said to be either kinetic energy or potential energy.
The kinetic energy of a particle of mass m and speed v is ½mv2. The kinetic energy of a system of particles is ½MV2 where M is the system mass and V is the speed of its center of mass. One part of a system's kinetic energy may be thermal energy due to disordered motions and vibrations of particles, on the microscopic scale of molecules, atoms, and even smaller particles.
The potential energy of a system is always due to some other system exchanging energy with it by forces moving the system or parts of the system. Potential energy is a way of accounting for the work done by or on another system interacting with the system of interest. Gravitational potential energy is the work we must do against the force due to gravity to move an object to a new position. Once we have accounted for the effect of other systems we can treat our system as if it were "isolated", which is often convenient.
Systems may exchange energy in two ways, through work or heat. Work and heat are never in a body or system, they measure the energy transferred during interactions between systems. Work always requires motion of a system or parts of it, moving the system's center of mass. Heating does not require macroscopic motion of either system. It involves exchanges of energy between systems on the microscopic level, and does not move the center of mass of either system.
