Aximar was a location, somewhere in the galaxy's Alpha or Beta Quadrants. At some point prior to the middle of the 23rd century, Aximar was the site of a military confrontation that resulted in an historic victory.

Garth of Izar wrote a textbook about the victory, titled Victory at Aximar. The volume was part of the collection of Cadet James T. Kirk in the year 2251. (TOS - Starfleet Academy novel: Cadet Kirk)

It is implied, since Garth wrote the book on the confrontation, that he was involved in the victory, possibly as the military commanding officer. However, since the conflict was not described in any way, it could also be possible that Garth was writing about another commander's victory. The name "Aximar" is very similar to "Axanar", which is another location associated with Garth's service career.