convention vs group meeting

convention and group meeting both are nouns.

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

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

Other hypernyms of convention include meeting.

convention (noun)	group meeting (noun)
the act of convening	a formally arranged gathering
orthodoxy as a consequence of being conventional
something regarded as a normative example
(diplomacy) an international agreement
a large formal assembly