It might be even more than that eventually, a truly independent gadget, but a vast majority of its current core functions — making calls, sending messages, getting information, even playing any third-party games — require your iPhone to be on, have Internet service, and be paired with the Watch via Bluetooth or a shared Wi-Fi network.
If you’re thinking about getting one, make sure you know that. It requires an iPhone 5 or later, and it can’t even be set up without one.