A radio tranmission modulation technique derived from AM.
AM produces a carrier frequency and two sidebands. If you suppress the carrier (saves power), you get double sideband, abbreviated DSB. (The carrier is reinserted at the receiver). If you suppress (filter) both the carrier and one sideband, you get single sideband (SSB).
Depending on which sideband is suppressed, you may need to receive either the upper sideband (USB) or the lower (LSB).