PIN vs personal identification number

PIN and personal identification number both are nouns.

Word	Noun	Adjective	Verb	Adverb
PIN	Yes	No	No	No
personal identification number	Yes	No	No	No

As nouns, PIN and personal identification number are synonyms defined as:

PIN and personal identification number: a number you choose and use to gain access to various accounts

Other synonyms of PIN include PIN number.

PIN (noun)	personal identification number (noun)
a number you choose and use to gain access to various accounts	a number you choose and use to gain access to various accounts