Definitions for "Subclassing"
Subclassing refers to an OO mechanism that allows one to collect a subset of members of a large class based upon a suite of specialized properties unique to only that subset of members. All members of the subclass also share the properties of the related superclass. Often subclassing is referred to as "generalization" or "specialization" because of the way one commonly identifies subclasses (subdividing groups already sharing properties based on other properties that they do not all share) and superclasses (grouping common properties into a superclass) in practice. It is important to note that subclassing is the paradigm followed in OOA/D, but it is implemented in OOP as subtyping. (See category on relationships.)
In Windows programming, a technique that allows an application to intercept and process messages sent or posted to a particular window before the window has a chance to process them. By subclassing a window, an application can augment, modify, or monitor the behavior of the window.
The act of modifying the standard behavior of an object provided by Windows. Visual Basic doesn't directly support subclassing.