GoKawiilAndroid Auto and Android Automotive sound like two names for the same product, which isn't exactly helping anyone. Thankfully, the difference is pretty simple.
The one that most drivers will be familiar with is Android Auto. The experience is powered by your Android phone, and a compatible car display provides you with a driving-friendly interface for navigation, music, messaging and supported applications. It's Google's response to Apple CarPlay and can be used via USB or wirelessly, depending on your phone and car.
Android Automotive OS (AAOS) is a different animal. It operates directly on the car's hardware, meaning there's no need for a phone to do the heavy lifting. It gets a little more complicated when Google built-in comes into the mix (as if the naming wasn't confusing enough), but that's another story.