The term junior officer is sometimes used to make clear that an officer in a military or para-military command is not in over-all command. The term senior officer is reserved for the officer in over-all command.
The term has a specific meaning in Russian military ranks, to encompas the range of ranks from "Junior Lieutenant" to "Captain".
The Junior Reserve Officer Training Corps (JROTC) is a program sponsored by the United States Armed Forces in high schools across the nation that train high school students in leadership and military sciences.
Each program is directed by a Senior military, naval or aerospace instructor, who is a retired officer, and an assistant military, naval, or aerospace instructor, who is a retired non-commissioned officer, warrant officer, or commissioned officer of lesser rank.
Junior ROTC units can also be found in military schools.