gathering vs congress

gathering and congress both are nouns.

Word	Noun	Adjective	Verb	Adverb
gathering	Yes	No	No	No
congress	Yes	No	No	No

As nouns, congress is a hyponym of gathering; that is, congress is a word with a more specific, narrower meaning than gathering:

gathering (noun)	congress (noun)
the social act of assembling	the social act of assembling for some common purpose
the act of gathering something	a meeting of elected or appointed representatives
sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching	a national legislative assembly
a group of persons together in one place