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.