Nothing, honestly. They are basically one and the same. Some people prefer to call them cookies and cream desserts, and some people Oreo. There are a ton of companies out there that produce cookies and cream desserts. There is some debate about which came first (kind of a chicken and egg thing happening). I didn't spend a ton of time researching it, but basically, it seems that everyone is claiming to have created the sandwich cookies. It's the Oreo brand that popularized them, so they're the ones we know today.