junior

• younger person; one having a lower rank or position; new arrival, one recently admitted; student in a class which is next below the last year
younger (placed after a name to indicate the younger of two who have the same name, esp. a father and son); having a lower rank or position; more recently admitted; of or belonging the class which is next below the last year (of a student)
someone who is junior holds a position that is less important than others in an organization or profession. adjective here but can also be used as a count noun. e.g. police officers later blamed their juniors.
if you are someone's junior, you are younger than they are.
when there are two people in one family who have the same name, junior is sometimes used after the younger person's name in order to prevent confusion.
in the united states, a student in the third year of a high school or university course is called a junior.