Ether

Ether is a term for pure magical energy. The city of Avalir is unique in its ability to collect and store this energy, and to return it back to the land in a ritual known as the Replenishment.

Ether can best be understood as magical potential within objects. One source of ether is magical objects, which Avalir breaks down for that energy; unneeded objects go to an arcane furnace to have the ether removed. It is then stored in the Etheric Net.

Laerryn Coramar-Seelie has a belt that is capable of storing ether, which mechanically allows her to restore spell slots.

Trivia
The term "ether" is possibly a reference to the classical element of aether, which was used to explain concepts in physics that were not yet understood at the time.