2.5 gen groups were the groups that debuted between 2nd and 3rd gen (according to google 2010-2013) that debuted later but didn't jumpstart a new generation.
so if the defining groups of 3rd gen are groups like exo, blackpink, twice, bts, etc. and the defining groups of 4th gen are now being established, who would you consider 3.5 gen?
groups that debuted later during 3rd gen, and may or may not be considered 4th gen