From Hidden Frontier
Major is a military rank, the equivalent of which is used by the service organizations of many civilizations. As a traditional grade, Major is a line officer of a fighting organization, below a Colonel and above a Captain. In comparison to naval ranking systems, this rank is equivalent to the naval Lieutenant Commander rank. Some rank systems include an additional rank, Lieutenant Colonel, that is superior to Major and inferior to Colonel.
This Starfleet Marine Corps rank is designated on the uniform collar by a two gold pips and one hollow pip.