PA system vs public address system

PA system and public address system both are nouns.

Word	Noun	Adjective	Verb	Adverb
PA system	Yes	No	No	No
public address system	Yes	No	No	No

As nouns, PA system and public address system are synonyms defined as:

PA system and public address system: an electronic amplification system used as a communication system in public areas

Other synonyms of PA system include P.A., P.A. system, PA.

PA system (noun)	public address system (noun)
an electronic amplification system used as a communication system in public areas	an electronic amplification system used as a communication system in public areas