Ensign junior grade

Ensign junior grade is a rank of officer in naval services and space forces, most notably the Starfleet of the United Federation of Planets.

An ensign junior grade is a variation of the most basic of officer ranks, a grade higher than any NCO or other enlisted personnel, and a grade below ensign in some rank structures. This grade of ensign rank is roughly equivalent with the authority of a lieutenant of military forces, but many services have no direct analog, with this grade falling below second lieutenant.

Ensign junior grade, at one point, had a specialized uniform insignia, a rank insignia worn on the Starfleet uniform of the 2350s, used for some time afterwards.That uniform design was one of a rare few that had a specialized insignia in the ranking system of the era. (FASA RPG module: Star Trek: The Next Generation Officer's Manual)

In 2376, Captain Mackenzie Calhoun of the USS Excalibur gave his son Moke, the rank of Ensign Junior Grade, in exchange for taking care of Xy. (NF novel: Being Human)

The source reference Officer's Manual was written from the point-of-view of the mid-2360s, meaning there is no confirmation whether or not this insignia was continued in later uniform styles, as no other canon or licensed source show any visual depiction of this rank's insignia.