Use this tag for all questions about scroll views on iOS. Do NOT use this tag for other platforms.
UIScrollView is the native scroll view system in iOS. It is part of Cocoa and UIKit. A number of other very common iOS classes, such as UITableView, are based on UIScrollView. UIScrollViewDelegate is the associated delegate.
Full Apple documentation for UIScrollView is at the usual Apple documentation site. It is on the internet. It can be found at https://developer.apple.com/reference/uikit/uiscrollview.
Use this tag only for the specific, iOS, UIScrollView class. For the native scroll views in other specific platforms, such as Android, use those tags.
If you genuinely have a rare, non-platform-specific, general conceptual question about scroll views, you could use the otherwise totally worthless scrollview tag.