An advertising ID is a unique user ID assigned to a mobile device or operating environment to help advertising services personalize their offers. It is used by advertisers and other third parties to track the users movements, habits, and usage of applications. The advertising ID is a user-resettable ID for advertising, provided by Google Play services. It is also used by Apple and Microsoft, who call their advertising ID the "Identifier for Advertisers" (IDFA) and "Microsoft Advertising ID," respectively.

The advertising ID is important for advertisers because it allows them to measure user ad activity on Android devices. It helps advertisers know when an ad has been viewed or clicked in an app, and when an ad causes a conversion. The good thing about the advertising ID from a marketers perspective is that it is semi-permanent and does not change unless users specifically take an action in their Android device settings.

To get the advertising ID in your apps, you can use the Advertising ID API. However, apps using a persistent ID other than the advertising ID may receive a policy violation warning via the publisher site or the email address used to register the account. If you receive a warning, you should ensure that any published APKs comply with the advertising ID related guidance in the Developer Program Policy.

It is important to note that users can choose whether to allow apps to track their advertising ID. For example, beginning with its iOS 14.5 software update, Apple allows its users to choose whether to allow apps to track their IDFA. With the release of Android 12, Google began allowing users to delete their advertising ID permanently. On devices that have this feature enabled, users can open the Settings app and navigate to Privacy > Ads. They can then tap “Delete advertising ID,” then tap it again on the next page to confirm.