An energy pile was an early to mid-23rd century term for the matter/antimatter reaction system on a starship.

In 2266, the Antares had a warped baffle plate on its energy pile shield, as noted by Charlie Evans. He "made it go away", causing the ship to explode, because he did not like the crew, justifying his act by stating, "It would've blown up anyway." (TOS: "Charlie X")