A subaltern is a military term for a junior officer. Literally meaning "subordinate", subaltern is used to describe commissioned officers below the rank of captain and generally comprises the various grades of lieutenant. In the British Army the senior subaltern rank was Captain-Lieutenant, obsolete since the 18th century.
The term is used in postcolonial theory to refer to the lower classes.
The word 'subaltern' coined by Antonio Gramsci.