A band is a range of frequencies in the radio electromagnetic spectrum. Different bands are reserved for different applications, such as radio broadcasting or citizen's band.
In the context of mobile telephony, a band refers to any range of frequencies in the radio spectrum's ultra high frequency (UHF) band. Telephony bands are regulated and licensed to operators that provide mobile phone services.
Techopedia explains Band
For example, the Global System for Mobile Communications (GSM) 1800 operates from 1710-1880 MHz. A 1710-1785 MHz band is used to send information from a mobile device to a base transceiver, while a 1805-1880 MHz band is used to send information in the opposite direction.
Normally, bands are auctioned by the government. When the government licenses a band to a mobile provider, the provider operates only in the specified band. Additional band operations require additional licenses.
Most modern mobile devices are known as multiband because they support multiple bands. There are three main types of multiband phones:
Dual band: Supports only two bands.
Tri band: Supports 850, 1800 and 1900 MHz bands.
Quad band: Supports the four GSM spectrum bands: 850, 900, 1800 and 1900 MHz.Some phones support bands supported by different standards. For example, a Nokia 6340i GAIT phone version supports 1900 and 1800 GSM bands, 1900 and 800 time division multiple access (TDMA) bands and the 800 advanced mobile phone service band. Having a mobile phone with a multiband feature is particularly useful for world roaming because countries employ different frequency bands.