MKV is Mastroska video belonging to Matroska that different from your regular video and audio compression format. MKV is a open source standard multimedia container format that can hold an unlimited number of video, audio, picture or subtitle tracks inside a file. Matroska are .MKV for video (and audio) and .MKA for audio-only files.
MKV has the futuristic design approach. Its features exceed even those of AVI and MP4 files. Its primary purpose is to create a unifying or universal format for multimedia storage with the benefit of being completely open source.