Heat. You have heard it before. You have used it. I have even used it. Do we need this word? No. Is this a useful word? No.
Let me start with the definition as usually stated in a physics type text: (this is from [dictionary.com](http://dictionary.reference.com/browse/heat))
*heat:* a nonmechanical energy transfer with reference to a temperature difference between a system and its surroundings or between two parts of the same system.
This definition is fine. It is not wrong, but is it needed? Not really. Couldn’t we just say energy transfer? Actually, I like to use this in the following equation:
In this equation (the work-energy equation) W stands for the work, and Q is typically referred to as “heat”. This equation is used for systems of particles, if you just have one particle, then the fundamental equation is:
So, expanding to macroscopic systems, Q is still work. Work is the only way to change the energy of a system. I like to call Q (like some textbooks do) as micro-work. Q is the work done on the system due to particle collisions from another object.
The other non-sciencey definitions are clearly wrong. The common usage of the word heat is also clearly abused. This can be seen in phrases like “add heat” or “remove heat”. Another poor usage (which I have used) is “heat this thing up” which implies heat is a verb.
Ok, then if we do not use heat – what then? I think if you want to talk about transfer of energy, say transfer of energy. If you want to use Q, call it microwork. If you want to talk about the energy something has because it is hot, say thermal energy.