Yeoman

Yeoman was a Starfleet title with administrative and clerical duties. Starfleet used different rates of yeoman including "yeoman third class" as seen with Tina Lawton. (TOS: "Charlie X") Some yeoman, such as Janice Rand, were enlisted personnel during their time in this position. However, a yeoman could hold the rank of an officer as seen with Martha Landon (TOS: "The Apple") and an unnamed yeoman assigned to the USS Enterprise-A, who wore an officer's uniform with the rank of lieutenant junior grade. (Star Trek V: The Final Frontier)

Janice Rand later underwent training to become an officer as well, but she no longer performed the duties of a yeoman. (VOY: "Flashback")

Given that Starfleet ranks typically correspond to those of the United States Navy, "yeoman" most likely refers to the job specialty, or "rating", rather than a rank of its own. A yeoman in this case is one who perform administrative and clerical duties, which fits the function of those referred to as "yeoman" in Star Trek.