• Component Object Model (COM) - A standard for the way different objects communicate across application boundaries.  COM provides an interface that works down to the binary level, which means that any COM component can communicate with any other COM component, at least to the point where they can interrogate each other to see if they support compatible methods.  Both OLE and ActiveX are based on COM.
  
  • COM Client - An application that hosts a COM component and makes use of the component's properties, methods, and events.  After adding a reference to a COM component, the client can create objects from the component's classes.
    
  • COM Component (Server) - A class library which gives the COM client the benefit of prewritten code.  Created using class modules.  Once a COM component is registered with Windows, its classes (properties, methods, and events) are made available for client applications to use.
    
  • COM-based objects:
    • ActiveX controls
    • Active documents
    • ActiveX-enabled applications (e.g. Microsoft Word or Excel)
    • ActiveX EXEs and DLLs (code components)
    • OLE items
  
  
• Class - In object-oriented programming, a category of objects.  For example, there might be a class called shape that contains objects which are circles, rectangles, and triangles.  The class defines all the common properties of the different objects that belong to it.
  
• Dynamic Link Library (DLL) - A library of executable functions or data that can be used by a Windows application.  Typically, a DLL provides one or more particular functions, and a program accesses the functions by creating either a static or dynamic link to the DLL.  A static link remains constant during program execution while a dynamic link is created by the program as needed.  DLLs can also contain just data.  DLL files usually end with the extension .dll, .exe, .drv, or .fon.  A DLL can be used by several applications at the same time.  Some DLLs are provided with the Windows operating system and are available for any Windows application.  Other DLLs are written for a particular application and are loaded with the application.
  
• Object - Generally, any item that can be individually selected and manipulated.  This can include shapes and pictures that appear on a display screen as well as less tangible software entities.  In object-oriented programming, for example, an object is a self-contained entity that consists of both data and procedures to manipulate the data.