Lunar Colonies was a location presumably on Earth's moon, Luna. Dr. Karen Patterson booked passage from Earth to Lunar Colonies on stardate 2716.6, and from there, travelled to Altair VI on stardate 2717.1. (TOS novel: Cloak)

It would seem, from context, that "Lunar Colonies" is a proper name for a single location -- perhaps a transit station -- rather than a reference to the colonies of the Moon collectively. It is also possible that "Lunar Colonies" could be on or near the moon of a planet other than Earth.