Direction Names Within a Galaxy
The galactic coordinate system is usually used for galaxies. It is based on the galactic plane — approximately where the galactic disc is.

It uses galactic latitude (for the y-value of the objects) and galactic longitude (x and z values, based on the disc).

There is also a supergalactic coordinate system used for superclusters.

Its equator is an invisible line called the supergalactic plane, which is the preferred distribution of galaxies in a supercluster.