When most people think about Google and VR, the first thing that comes to mind is typically Cardboard. Google worked hard to make an inexpensive VR platform that would work on basically any phone, and the popularity of the platform exploded overnight. Cardboard was included in magazines and newspapers for free, and the ability to consume video in VR quickly became something anyone could participate in, but only for a few minutes at a time. It's success made one thing abundantly clear — standards needed to exist in order to increase the quality beyond a passive viewer. Those standards are called Daydream, and it works a little differently than Cardboard.
Instead of a headset any phone can work in, Daydream is a series of rules for creating high quality VR that can be enjoyed for hours instead of minutes. These rules include specific processor types, display capabilities, and motion sensors in the phone that work with the other hardware to create a high-end experience. In a sense, Google is taking the things that Samsung and Oculus made work so well with the Samsung Gear VR and applying it to many phones inside of many headsets. In short, a higher quality version of Cardboard.
What separates Daydream from any other mobile VR experience is the Daydream Controller. This is a small Bluetooth controller that can be used in Daydream, and when you look down you can actually see a virtual representation of the controller positioned wherever your hand is resting. As you move your hand around, the controller moves to match. You can use this controller as a laser pointer, a sword you can slash, or a menu system you can control by clicking and waving the controller around.
The first headset for Daydream was made by Google, and called Daydream View. Originally this headset only worked with Google's Pixel and Pixel XL phones, but Google has been working with hardware partners to quickly add more phones to the Daydream-Ready list. Google's partners are also free to make their own version of Daydream View if they see fit, and several have announced plans to do exactly that.