COM is a technology that allows objects to interact across process and machine boundaries as easily as objects within a single process interact. COM enables this by specifying that the only way to manipulate the data associated with an object is through what is called an interface on the object. When this term is used, it refers to an implementation in code of a COM binary-compliant interface that is associated with an object.
Talking about an object that implements an interface means that the object uses code that implements each method of the interface and provides COM binary-compliant pointers to those functions to the COM library. COM then makes those functions available to any client who asks for a pointer to the interface, whether the client is inside or outside of the process that implements those functions.
For more information, see the following: