It is a new model of Google to prevent Android applications from accessing personal information while showing ads. Each phone is given such a random number that can be reset at will. Advertising behaviors are determined through this id. This id is shared by apps.
This code is not used in your browser sessions like Google Chrome. You are tracked with standard cookies.
The advertising ID is a user-resettable, unique, anonymous ID for advertising, provided by Google Play. It gives consumers control over privacy and advertising tracking and provides developers with a simple, standard system to continue to monetize their apps.