system.mof

Managed Object Format file Reference

A .mof file contains class definitions in the Managed Object Format. The syntax comes from the Common Information Model of the DMTF. On Windows, the mofcomp tool compiles these files into the WMI repository. The files define classes, properties, and methods for management data. Software installs .mof files to register its management interfaces.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.