The Elder Galaxy is a Galaxy that exists in The Universe. It is quite small, and it is elliptical, so there are not many planets there, however, it does contain several areas containing magical properties as well as fluctuations in space and time. The Pantheon of the League are believed to reside here, as well as Middle Earth and a planet called Nirn, where the famous Tamrielic Portals to Oblivion are located, amongst many other things.
Aedra and Daedra rule here under the Pantheon, however their influence is limited outside the Elder Galaxy due to their reliance on background Magicka to survive.
The League use it to access the Distortion World.