RPM vs CPM is two ways of measuring ad money per 1,000 views.
CPM (cost per mille) is what advertisers pay per 1,000 ad impressions, before YouTube's share. RPM (revenue per mille) is what you earn per 1,000 views, after YouTube's share and across all revenue types, including views that showed no ad.
RPM is the number that matters for creators. Indian audiences generally have lower RPMs than US or UK audiences, and RPM varies a lot by niche and season.