A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose. Examples include:
Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers.
Note that as a matter of physics, bands are divided at wavelengths of 10n metres, or frequencies of 3×10n hertz. For example, 30 MHz or 10 m divides shortwave (lower and longer) from VHF (shorter and higher). These are the parts of the radio spectrum, and not its frequency allocation.