Following up on a promise that the company made earlier this year at their annual I/O conference, Google is launching Google Play services v1.0. To put it in simple terms, it's designed for developers who want to integrate Google services into their Android apps. With the new integration, apps can now include Google+ features, as well as OAuth 2.0 functionality.
The platform consists of two parts: a services component that runs on the device, and a client library that developers package with their apps. The services component communicates with the Google service that the developer wants to use and requests information from the client library. The service component is available as an APK through the Google Play store.
The client library includes Google+ sign-in capabilities and +1 APIs, as well as OAuth 2.0 functionality. OAuth 2.0 is particularly important in this case because it offers both scalability and better security. There's no need to tack on more passwords than usual with the new OAuth, since it does a good job at offering improved security minus all the passwords.
Google Play services will cover devices running Android 2.2 Froyo and later, and they must have latest version of the Google Play store installed. The rollout of these services could take up to a week, and Google is advising app developers not to do anything until the rollout is complete, which is probably driving some devs crazy already. However, they can at least get started and download the required SDK and such in the mean time.