Introduced in April 2021 with the release of iOS 14.5 and iPadOS 14.5, Apple's ATT framework requires that all apps on iPhone and iPad ask for the user's consent before tracking their activity across other apps. Apps that wish to track a user based on their device's unique advertising identifier can only do so if the user allows it when prompted.
When Apple dropped App Tracking Transparency (ATT) prompts in iOS 14.5 back in 2021, it was a watershed moment for user privacy within third-party applications. Nothing like it had existed prior. The initiative gave iPhone users control over whether their in-app data could be aggregated and shared with third parties for advertising or other various purposes. Still, today, I often find comments online from people who don't really know what it does and find the wording very taboo.