advertising vs promo

advertising and promo both are nouns.

Word	Noun	Adjective	Verb	Adverb
advertising	Yes	No	No	No
promo	Yes	No	No	No

As nouns, promo is a hypernym of advertising; that is, promo is a word with a broader meaning than advertising:

advertising: a public promotion of some product or service
promo: a message issued in behalf of some product or cause or idea or person or institution

Other hypernyms of advertising include packaging, promotion, promotional material, publicity.

advertising (noun)	promo (noun)
the business of drawing public attention to goods and services	a message issued in behalf of some product or cause or idea or person or institution
a public promotion of some product or service