If the filename was generated by a ripping tool and you need to know how to use it:
MKV is a "container" format that can hold multiple video, audio, and subtitle tracks. Not all default players support it well.
The definitive set of tools for Matroska files. Use the "Multiplexer" tab to drag and drop your file, uncheck the tracks you don't want, and click "Start multiplexing" to create a new, clean version.