Component Object Model or COM was invented by Microsoft in 1993. It included a number of features that allowed applications to communicate with one another in a language agnostic fashion. A number of technologies fall under the Com umbrella including OLE, ActiveX, DCOM, and COM+.
Many of the features found in COM have since been replaced by .NET and the CLR. With languages sharing a common runtime, COM's method for exposing object libraries is no longer needed. .NET remoting replaces DCOM, and unlike ActiveX controls, downloadable libraries written in .NET can be verified for safety.
This is all theory. In reality, the picture is much more complex. The COM based language, Visual Basic, is still a major platform for many companies even though it is no longer supported in any meaningful fashion. And COM is still the technology of choice for Microsoft Office as wells as countless other applications. Even Windows Vista exposes some new functionality via COM libraries.
So the question remains, is COM a dying technology or something that will be seen for many years to come?