A situation wherein there is equilibrium of energy, with in the system. Short of pocket dimensions, this is almost never seen in real life.
To be more specific, it is when energy in a system constantly loops around, instead of being expended outward.
- Plasma Cells: The plasma they contain runs through the Plasma Coils that generate the field that contains the plasma. While there is entropy, it would take thousands, to millions of years to run out, depending on the cell.