Phonograph cylinders were introduced by Thomas Edison in the late 1800s as the first system for the distribution of recorded sound. They later had a "format war" with disc-shaped gramophone records, which ended with the discs winning out. These (as well as other formats such as the dictabelt) consist of a groove representing analog audio, played by a needle tracking it.
As the contents of most phonograph cylinders had been believed to be in the public domain now due to age (though the actual situation for sound recording copyright is more complicated, and the Music Modernization Act actually gives such old recordings a US copyright that lasts until January 1, 2022), many have been digitized into computer sound files which can be freely downloaded on the Internet.
Most cylinders rotate at 160 RPM, but some other speeds such as 120 and 144 were used in the earliest times.