If there are no Abstract classes, why do they refer to them in the documentation?

I was looking through the Apple documentation on the UICollectionViewLayout and saw this:

An abstract base class for generating layout information for a collection view.

Source

As you can see, they refer to this as an abstract class, and yet, there are questions like this littered all over SO:

Abstract class in Swift

Abstract classes in Swift Language

In all of these, the answers say that there is no concept of "abstract class" in Objective-C or Swift.

If this is true, why do they continuously refer to it?