What does the term ‘Dolby B’ or ‘Dolby C’ printed on tape recorders and other sound systems refer to?

‘Dolby B’ and ‘Dolby C’ are consumer audio noise‑reduction systems developed to reduce tape hiss and improve playback/recording fidelity on magnetic tape formats such as compact cassette. Dolby implementations apply companding (compression on record, expansion on playback) often using a sliding‑band approach (Dolby B uses a single sliding compression‑expansion band) to lift low‑level treble signals above the noise floor and restore them on playback, thereby lowering perceived noise. They are part of the family of Dolby noise‑reduction technologies rather than modulation schemes or power options, so the correct interpretation is a noise‑reduction circuit/system [1].

Sources

1. [1] https://en.wikipedia.org/wiki/Dolby_noise-reduction_system