lunch meeting vs meeting

lunch meeting and meeting both are nouns.

Word	Noun	Adjective	Verb	Adverb
lunch meeting	Yes	No	No	No
meeting	Yes	No	No	No

As nouns, meeting is a hypernym of lunch meeting; that is, meeting is a word with a broader meaning than lunch meeting:

lunch meeting: a meeting for lunch; usually to conduct business while eating
meeting: a small informal social gathering

Other hypernyms of lunch meeting include get together.

lunch meeting (noun)	meeting (noun)
a meeting for lunch; usually to conduct business while eating	the social act of assembling for some common purpose
	the act of joining together as one
	a casual or unexpected convergence
	a formally arranged gathering
	a small informal social gathering
	a place where things merge or flow together (especially rivers)