The flag officer rank of general was used by General Casey, commanding officer of the MACOs who were assigned to the Enterprise. This rank was approximately equivalent to an Starfleet admiral. (ENT: "The Expanse")
It was not revealed if the MACO infrastructure used any separate grades of general rank, and no general's rank insignia was ever made for the series. Based on the rank insignia that was shown, a "general" would be one, two, three, or four stars.
The rank is also used in the Klingon Defense Force and was equivalent to Admiral in Starfleet.