POB vs PO Box

POB and PO Box both are nouns.

Word	Noun	Adjective	Verb	Adverb
POB	Yes	No	No	No
PO Box	Yes	No	No	No

As nouns, POB and PO Box are synonyms defined as:

POB and PO Box: a numbered compartment in a post office where mail is put to be called for

Other synonyms of POB include call box, letter box, Post-Office box.

POB (noun)	PO Box (noun)
a numbered compartment in a post office where mail is put to be called for	a numbered compartment in a post office where mail is put to be called for