COM: Component Object Model
the basis of OLE (Object Linking and Embedding) and Active X technologies is the Microsoft software component model. COM components are encapsulated objects that have a set of structured interfaces. This standardization enables different applications or components to communicate freely with one another.
Distributed Component Object Model provides distributed services to COM. Such services allows various components to communicate easily across a network. As a single vendor standard DCOM represents a uniform interoperability mechanism.