I had been telling me daughter that energy is the capacity for doing work. However I realised this isn't really accurate, so I've been googling around for a better definition, without much success so far. My confusion is summarised in this ChatGPT session.

Can anyone help me understand what "energy" really is?

@jh
I too get caught in loops with these things. What is energy? The currency you can spend to do work. What is work? That which takes expenditure of energy to accomplish ...or, better, movement accomplished against resistance. What is resistance? A counter force. How are forces produced? By systems which have the energy to move things .. and so on.