The term auxiliaries comes from latin auxilia (help). It is mainly used for bodies of men supporting a main military or paramilitary force, particularly in the following instances:

• United States Coast Guard Auxiliary
• Roman auxiliaries, non-citizen troops supporting the Roman legions.
• British soldiers in the Irish War of Independence who became famous for their brutality
• members of the Auxiliary police

Other uses:

• Auxiliaries can also be used to refer to Auxiliary verbs in linguistic contexts.
• Chiral auxiliaries are chemical compounds used in chiral synthesis

Auxiliartruppen | Auxilia