group meeting vs gathering

group meeting and gathering both are nouns.

Word	Noun	Adjective	Verb	Adverb
group meeting	Yes	No	No	No
gathering	Yes	No	No	No

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

Other hypernyms of group meeting include assemblage, assembly.

group meeting (noun)	gathering (noun)
a formally arranged gathering	the social act of assembling
	the act of gathering something
	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching
	a group of persons together in one place