Static vs dynamic type

In Swift we can determine type of variable by type(of:) and Mirror(reflecting:).subjectType.

Documentation about Mirror.subjectType says:

The static type of the subject being reflected.

This type may differ from the subject’s dynamic type when self is the superclassMirror of another mirror.

I did not find docs for type(of:) but the proposal says that it's replacement for .dynamicType property.

So we have dynamic and static types. What the difference between them and in what circumstances does it show up?