4 links have been added on this idea.
  1. Same. interchangeable means the same in a way.

  2. Hard to find a definitive answer according to this https://www.askamathematician.com/2010/01/q-is-it-true-that-all-matter-is-simply-condensed-energy/

  3. Matter isn’t stored energy but t does have energy, called “rest energy.” What distinguishes matter-energy from other forms of energy is that all matter has inertia and is subject to the force of gravity when at rest as well as when in motion.