At its core, MKVCinemas was an illegal streaming and downloading platform that provided free access to a vast library of movies and TV shows without the copyright holders' permission. The name "MKV" comes from the Matroska Multimedia Container, a popular video file format, which the site used to distribute its pirated content. It became popular due to its extensive library, easy-to-use interface, and the ability to download high-quality movies for free.