OK...so what is "ER", then? Do you mean "Earth radii"? That is a very unusual way of putting it. Can't say I've ever heard it before. I have heard of "Earth diameters" in reference to the sizes of other planets, notably the smaller exoplanets.

The Earth-Moon distance is usually given as a direct distance in kilometers, or miles for the metrically disabled.

"LD" (Lunar Distance) is often used in reference to some object, such as an asteroid, that is passing very close to the Earth-Moon system.

When referencing the variation in the Earth-Moon distance due to the Moon's elliptical orbit, perigee and apogee are used (for near and far points respectively).

Brian