The Identifier for Advertisers (IDFA) is a unique identifier consisting of a string of 32 digits. It is given by Apple randomly to each iOS device including mobile phones, tablets, and iPads. It is crucial for mobile attribution because it identifies, tracks, and measures users’ behavior, app usage, and interaction.

IDFA helps mobile advertisers to create and optimize personalized ad campaigns and to track the ad campaign performance. 

Mobile users can reset their IDFA in order not to tracked by mobile advertisers and attribution tools. 

On 22 June 2020, in Apple’s WWDC (World Wide Developer Conference), Apple announced an update about IDFA. With iOS 14, developers will be required to ask users for permission to track them and to summarize their privacy information. To read the details about the update, you can read this article.