COM is nothing more than communication between applications. DDE, OLE, ... Are the same things but they've extended the communication down to the object level. Which means you can create word objects, excel objects, etc... from your VFP application, and modify their properties/call their methods, use them for what ever you need them. Some applications that are COMpatible with this standard are:
Word, Excel, Outlook, VB, Visio, etc...

Again PCMCIA is the keyword here. (People Can not Memorize Complicated Industrial Abbreviations)