petting zoo vs aggregation

petting zoo and aggregation both are nouns.

Word	Noun	Adjective	Verb	Adverb
petting zoo	Yes	No	No	No
aggregation	Yes	No	No	No

As nouns, aggregation is a hypernym of petting zoo; that is, aggregation is a word with a broader meaning than petting zoo:

Other hypernyms of petting zoo include accumulation, assemblage, collection.

petting zoo (noun)	aggregation (noun)
a collection of docile animals for children to pet and feed	the act of gathering something together
	several things grouped together or considered as a whole