COM stands for Component Object Model. Essentially, it is the protocol that allows a component to be used by a program. The COM protocol defines the rules for creating using a COM object. A COM object is simply a program written using the COM protocal. In Visual Basic, this is done by creating a Dynamic Linked Library, or DLL. Visual Basic will automatically insert the COM protocols for you. DLL's are used in nearly all programs written today. A DLL contains code that can be executed just as with any other computer program. The difference is that a DLL is in a format that can be used by any program that chooses to use it. A DLL is specifically designed for this type of re-usability. Instead of incorporating code directly into a program, it is stored in a library, then dynamically linked to by any program that chooses to use it. To avoid confusion with the terminology, I will refer to these objects as DLL throughout the rest of the lecture.