Single sideband modulation or SSB is derived from amplitude modulation (AM) and SSB modulation overcomes a number of the disadvantages of AM.
More expensive CB and Amateur radios have SSB which stands for "Single SideBand". The two options available are USB (Upper Side Band) and LSB (Lower Side Band).
More experienced CB/Amateur radios operators use these bands as they produce more power when transmitting and receiving.
When using these bands you need to "clarify" the incoming signal so you can understand what the other operator is saying otherwise they will sound like Donald Duck. You also need to clarify yourself making sure that you are on the same frequency as the person you want to speak to. The more expensive radios have frequency displays which tell you the exact frequency that you are on. This helps to make sure that you are "on frequency" when receiving and transmitting.