COM -- http://en.wikipedia.org/wiki/Component_Object_Model
http://www.webopedia.com/TERM/C/Comp...ect_Model.html

DCOM -- http://en.wikipedia.org/wiki/DCOM
http://www.webopedia.com/TERM/D/DCOM.html

These explanations relate to all MS technologies, not only VB. Do you want specifics on implementation of COM/DCOM in VB?