COM is a technology which allows the reuse of code written in any language (by any language) using a standard calling convention and hiding behind APIs the implementation details such as what machine the Component is stored on and the executable which houses it. It can be thought of as a super Remote Procedure Call (RPC) mechanism with some basic object roots. It separates implementation from interface.
COM encourages versioning, separation of implementation from interface and hiding the implementation details such as executable location and the language it was written in.
COM functions are only available on the Windows version of PHP.
These constants are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.