An ERP often includes (some approximation of) a WMS (usually as an addon or module or such), but usually not the other way around. There's usually overlap (like inventory and order management), but a typical ERP doesn't handle the minutiae of receiving/picking/packing/shipping like a WMS does (and when an ERP does attempt those things, it's rarely done well - though to be fair there are about as many shitty standalone WMS implementations as there are shitty WMS-as-ERP-addon implementations).