So let’s start with more scientific, philosophy questions…
What is heat? We can feel heat, we can measure it we can even generate heat… but do we ever ask ourself what is heat?
Heat is a property of energy.
And energy is an axiom. It is something true a priori.
heat is an form of energy which can not be taken as a substance because it can be transform into something which can not be a substance.
Heat is a byproduct of the energy in a system. It’s formed by atoms moving. What we generally refer to as heat is really a difference in heat. That’s what we actually can measure/feel.
You could say it is movement or change in anything - from very samll (smallest actual or currently theoretical particles) to the scale of the Universe perhaps 
Could we consider changes / oscialltions of space time a form of heat?
Heat is a form of energy, and its always refers to the transfer of energy between bodies. The energy of a body increasing its temperature and volume. Energy can take many different forms & it can change from one form to other one, not to energy contained within the systems.
Form of an energy 
Check it out, dude. Heat can be really hot and make things disappear, man.
Heat is energy produced in thermodynamics. It flows in spontaneity from one medium to the other with the variation of temperature. Heat is controlled by temperature and the variation therefore fluctuates.
Its what cooks our veggies!