I want to hijack it and add....
Couple of points along the same lines that I always like to explain to people.
The familiar E=mc^2 we all know - people like to say that means that the energy in a system is equal to the mass times the speed of light (squared) - if we convert between the two. Which is true..... but it's also saying something else. In this formula, energy is measured in joules, and mass in kilogams - the speed of light in meters per second. Importantly, notice the c^2 is a constant - it's there for unit conversion. What we really have is a statement that energy=mass. Energy and Mass are the same thing.
In the same line - there's no such thing as "pure energy" (if I'm wrong, someone educate me, I'm all ears) - people have a hard time with this. Energy is a property of a system that can be calculated. "pure energy" doesn't exist. Radiation is not what we mean by "energy" (though obviously it's got energy) - energy is a property that we can calculate and work with, and a rather important one at that.... but it's not a "thing" or "stuff" or "non-stuff" that moves around... it's a property of a system that can be calculated.