进口的基础。h,但使用:NSObject

I am a bit confused what the ": SuperClass" is for. Let say I have a model class called MyClass, which is subclass of NSObject. I write in its interface that the class is subclass of NSObject, but actually I almost never import only NSObject header file. What I import is whole Foundation.h precompiled header file. I am a bit confused what the ": SuperClass" is