An MKV file is a multimedia container format that allows you to store an unlimited number of video, audio, image, or subtitle tracks in a single file. It is similar to other containers such as AVI, MP4, and Advanced Systems Format (ASF), but its specifications are fully open and its implementation consists mostly of open-source software. The format is widely used for storing movies, TV shows, and other multimedia content. Key features of MKV files include:

• Versatility: MKV supports a wide range of codecs, making it compatible with various media players and devices.
• Multiple streams: It can contain multiple video, audio, and subtitle tracks in a single file, making it convenient for users who prefer different languages or subtitle options.
• Chapter support: The format supports chapter points, allowing users to easily navigate through the video file.
• Open-source: MKV is an open-source project, which means its development is driven by the community, ensuring continuous improvements and updates.
• Error recovery: The format is more resistant to errors than other formats, meaning that it can recover playback even if the file is corrupted.

MKV files are not an audio or video compression format, but rather a container format that can incorporate audio, video, and subtitles into a single file, even if those elements use different types of encoding. While MKV files are not supported by all programs, there are many open-source media players available that can play them, such as VLC or Miro.