But then, someone once asked me 'what is energy?' So I rattled through the whole orthodox list, mechanical, kinetic, potential, electrical, heat, audio - and how each form may be transformed into another form. But then, the question was repeated 'So ... what is energy?'
'Ummm, matter moving in space, relative to some other matter.' Doesn't apply to potential, that's an object in a field. That snow and those boulders up the hill aren't moving relative to me ... but could be, any minute now.
In the end, there's matter moving (or not, relative to me) in space. The rest of what's 'real' is in our minds - each of which is different.