What is a 'sub-class' mean

I was going thru a book and he wrote a class in a class and it looked it like this..

Public class Request
Public class parameter
private m_paramName as string
private m_Paramvalue as string

Public property ParamName as string
....
....
end property

End class

End class

What does it mean by subclass? I am seeing the subclass first time...any advantages?

thanks

Generally the .NET term subclass means a class that inherits from another class. Placing the class inside another one is not the same as inheriting from it though. Placing one class inside another isn't much different than placing it outside the class, except that it changes the namespace or the nested class and the nested class can access any shared private variables in class its nested in. When a class is derived or a subclass of another it automatically gets all of the parent or superclass' properties, methods, and events.