Does Kusama run on Polkadot?

Excuse me, could you clarify something for me? I've been reading about Kusama and Polkadot, and I'm a bit confused. Does Kusama actually run on Polkadot's blockchain or network? I understand they share some similarities and goals, but I'm not entirely sure how they relate to each other technically. Could you please explain this in a simple way? Thank you in advance for your help.