CB stands for "Citizen's Band" radio. It got that name because its main idea is to be a kind of radio service anyone can use. Depending on the country you live in, it is either a minimally-regulated or an unregulated set of radio channels used for short-range (local) communications. Many people use CB radios in their vehicles, homes or both.
Citizen's Band refers to a range of radio frequencies that lie between the short-wave broadcast signals and the 10-meter Amateur radio bands. These frequencies are divided into 40 channel starting from 26.965 MHz up to 27.405 MHz in 10 KHz steps.
CB (Citizens Band) Radio is an unlicensed service. Since the early 1980's, the FCC stopped requiring licenses for USA CB radio use. Users must still abide by all the FCC rules regarding the CB Band, however. The maximum allowable power for a CB radio is 4 watts (mandated by FCC). Repeaters are not allowed on CB radio.
"SideBand" (SSB) is a mode capability found in higher-end CB Radios. You will have access to the Upper & Lower Sideband Modes (USB, LSB), on each of the 40 channels, in addition to the "Regular" (AM) mode.
If you want to talk farther with a more efficient signal, Single Side Band is the way to go! You can usually expect an increase in range, & less noise on SSB, than on the "standard" AM 40 channels. FCC allows CB radios to have 4 watts of AM power, but up to 12 watts of SSB power.
A few CB's may seem to claim 5, or even "7 watts of output" on the box. This is misleading, it actually refers to the Audio power sent to it's built in speaker, "input" power, or some other nonsense that has nothing to do with the actual transmit output to the antenna, which is still 4w or less in that radio.]
A citizens band (CB) radio antenna is a device designed to do two things: It captures radio-frequency signals that are then converted to electrical signals by the receiver, and it takes electrical signals from the transmitter and converts them into radio-frequency signals. This second function is where tuning comes into play, because an antenna has to radiate radio-frequency signals, something that's done best when the length of the antenna precisely matches the wavelength of the transmitted radio frequency.
It is a radio system that is for the personal use of radio equipment. It is for local and national communications, and in some cases, internationally. It is not intended for commercial use, some communities use it as local town security where the police monitor a channel for citizen emergency calls. Some countries restrict communication distance by law!
The CB Radio Service has proven useful in disaster situations, both small-scale (for example, for a stranded motorist) and large-scale (such as after a hurricane or during a flash flood). An organization of expert communicators known as the Radio Emergency Associated Communications Teams (REACT) provides communications support in emergency situations. Channel 9 (at 27.065 MHz) is monitored by members of REACT, and is recognized as the CB emergency channel in the United States.