Corporal

Corporal is a military rank, the equivalent of which is used by the service organizations of many civilizations. As a traditional infantry grade, Corporal is an enlisted rank in a fighting organization, below a Sergeant and above a Private (which is only an actual rank in some cases). In comparison to naval ranking systems, this rank is marginally equivalent to the naval Petty Officer or Yeoman ranks.

This grade exists in some form in many rank arrangements, such as the Bajoran Militia and the Earth MACOs in the 2150s.

From Memory Alpha -- the free Star Trek reference