What is the Google Advertising ID?
The Google advertising ID is a string of 32 numbers and lowercase letters that identifies an Android device like a smartphone or a tablet.
GAIDs identify one unique device. They are created randomly by Google, but users can reset the GAIDs of their devices or disable them altogether to exclude their devices from tracking.
The pendant of the GAID for iOS devices is the IDFA.
Why is the GAID important?
GAID tracking enables app owners and ad networks to analyze their traffic and attribute users to specific traffic sources as it is the most precise tracking method for Android devices. Thus, it is the default method used by tracking providers.