First, a bit about terminology. Many words have different meanings. Take the word imaginary, for example. To a mathematician, there is nothing wrong with an imaginary number. It simply represents a particular type of number that is not on a regular number line, for example a number such as the square root of negative 1. To a physicist, an imaginary quantity may represent something that can not be represented by physically measurable units - to many physicists imaginary quantities are only math. "Don't be too hung up on imaginary portions of the equations because 'it's just math', they say. This philosophy trickles into the engineering field - especially electronics. Almost every equation used is complex - it has both a real and an imaginary component, but as I've said before, engineers routinely ignore the imaginary part of the equation and everything still works. The medical community regards an appendix the same way an engineer regards the imaginary side to an equation. Like an appendix, the imaginary portion is there, but useless and can be thrown away with no consequence. Surgeons will remove your appendix automatically if they go into your gut. Then there is the common meaning of the word imaginary, the way someone not in a technical field may use the word.
Other words get the same treatment. I have already used many of these words - virtual, complex, and real, for example. They all have many, equally valid definitions. I propose two other words that fit this confusing zoo of words: Information, and Nothing.
Information can be a really confusing word. The way I use the word 'information' is simply that which causes change. When the universe transfers information, you know about it because you can detect a change in state. Sometimes we use the words information and signal interchangeably. But, signaling is more appropriately defined as a method of transferring information. A signal usually has energy as a component, like in an electromagnetic (EM) wave. Your radio would be very boring to listen to if audio information couldn't be mixed with a higher frequency carrier wave. Though in this example, the EM wave propagating through space is made of energy, the information it carries is not. The information carried on an EM wave can be more accurately thought of as a time varying change in entropy. This shows that the words 'signal' and 'information' can mean different things. Now, why should I be so nitpicking about these particular words? Because, taken as a whole, The act of transferring information through a signal can define a work function. Information can define how much work is done per unit of time and a signal can define the way that work is done. Usually, energy can be defined as a work function, but we have already seen that under quantum physics, probability may also define a work function, irrespective of energy.
Nothing is even more abstract. We can't detect it. That seems to be a good definition of Nothing - Nothing doesn't mean there is nothing there, it just means we can't detect it. A bit over a century ago, radio waves would have qualified as 'Nothing' because they couldn't be detected. It certainly fits the definition for a P2 wave today. If you can't detect it, it doesn't exist i.e. it is nothing. (At least, until a way is found to detect them). This defines Nothing, but does NOT identify it. Like energy, Nothing can not be identified. Also, like energy, we can work with Nothing without knowing what it is...