The document defines and describes the history and features of the walkman, a portable cassette player released by Sony in 1979 that became hugely popular during the 1980s and 1990s for listening to music on the go. It details the internal components and controls of walkmans, as well as the cassette tapes they used. The document also notes how walkmans have been imitated in various other products and mentions some fun facts about their cultural influence and appearances in media.