IDE- Integrated development environment - the Delphi or CBuilder 
       development interface
  VCL - Visual Control - a component that contains executable code
        and data.  They are distributed in a set of files. Once 
        installed into your IDE, they can be dragged from your 
        component palette to one of your forms.

  VCLs interface with your code in these 3 ways:

  Properties - settings that tell the VCL how to perform it's 
        actions.  These can be set at design time in the Property
        Inspector, or at run time with Pascal/C++ code.
  Methods - these are functions/procedures that must be called
        by your Pascal/C++ code to perform actions.
  Events - these are calls to functions/procedures that you
        define in your code.  These calls execute automatically
        depending on certain key actions occuring.  The function/
        procedure that is called is the "event handler".  For
        example, an "OnMessage" event will call it's associated
        function/procedure (set via the Object Inspector) whenever
        the DLLs want to send the user a message.