Sublieutenant

Sublieutenant, also called Lieutenant Junior Grade, was a naval rank junior to lieutenant.

Galactic Empire
Sublieutenant was an Imperial Navy rank immediately above Ensign and below Lieutenant.

Ensigns were promoted to Sub-Lieutenant upon receiving certain command training and has proved their worth to their commanding officer through successfully managing given tasks and assignments. Sub-Lieutenants generally did not receive any command authority in the Navy, and was instead used for organizational means. Their only real authority was over Ensigns and non-commissioned officers, and instead just paved a way towards Lieutenant.

New Republic
The rank was used by the New Republic Starfleet for junior officers, except it was known as Lieutenant Junior Grade.