The Component Object Model (COM) is a standard for creating binary software components that can interact. It enables one applications (clients) to use capabilities of other applications and other software components (servers).
COM is the foundation technology for Microsoft's OLE (compound documents), ActiveX® (Internet-enabled components), as well as others. Automation (OLE automation) is COM-based technology that enables applications to provide objects in a consistent way to other applications, development tools, and macro languages. Part of Windows operating system features, that programmers can use, is based on COM, and cannot be accessed with Windows API (dll) functions. Some applications also provide COM objects. For example, you can use Excel capabilities from QM. You can also use standalone ActiveX components that can be downloaded from the Internet.
In general, a COM object is made up of a set of data and the functions that manipulate the data. These function sets are called interfaces, and the functions of an interface are called methods and properties. These functions can be accessed only through a pointer to the interface (in QM known as interface pointer variable).