single side band modulation

This comes from the early days of radio communications. It is also short for Single Sideband Suppressed Carrier or SSBSC. This is heterodyning the audio to the final frequency. This produces the narrowest bandwidth compared to AM and DSBSC. This is mostly used on HF. It gives about 6 dB SNR improvement over AM. This is the same improvement as DSBSC. Some people quote an additional 3 dB for SSBSC but this is not true since in demodulation of DSBSC the two sidebands add in phase and the noise from both sides of the suppressed carrier add uncorrelated.

In SSB the bandwidth is less than 3kHz (audio) so you can allocate a lot of channels spaced by, say 5kHz. Because you transmitt only 1 side of AM modulated signal and no carrier it is a power efficient transmission.

I forgot to add that SSB is used in FDM carrier telephone systems. This was started about 75 years ago. SSB over HF was later in coming and was phased in from 1955 to 1965 in round numbers.