Wikipedia
Magnitizdat (, from the Russian words for "tape recorder" магнитофо́н ), and "publishing" изда́тельство ) was the process of re-copying and self-distributing live audio tape recordings in the Soviet Union that were not available commercially. It is similar to bootleg recordings, except it was often sanctioned by the performers (who did not expect to make money from these recordings anyway) for the purpose of circumventing Soviet political censorship and making their work as well known as possible.
The process of magnitizdat was less risky than publishing literature via samizdat, since any person in the USSR was permitted to own a private reel-to-reel tape recorder, while paper duplication equipment was under control of the state.
Magnitizdat was the main method by which the songs of Russian bards such as Bulat Okudzhava, Vladimir Vysotsky and Alexander Galich or punk bands like Grazhdanskaya Oborona made their way around the Soviet Union and abroad. Magnitizdat was also used to distribute lectures with anti-Soviet content.