The higher their Rating Deviation (RD) value, the more the rating will change after a game. A high RD value basically is a indicator of an unstable rating, either do to not many games in a given pool or not enough recent games in that pool.
https://support.chess.com/customer/en/portal/articles/1444777-how-do-ratings-work-
notice that some rating numbers jump up massively like
902 then 997 in one completed game of 10min blitz.
how come?