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.
Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges.
To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.
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.
As a matter of convention, 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.

Band name	Abbr	ITU band	Frequency and wavelength in air	Example uses
			< 3 Hz > 100,000 km	Natural and man-made electromagnetic noise
Extremely low frequency	ELF	1	3–30 Hz 100,000 km – 10,000 km	Communication with submarines
Super low frequency	SLF	2	30–300 Hz 10,000 km – 1000 km	Communication with submarines
Ultra low frequency	ULF	3	300–3000 Hz 1000 km – 100 km	Submarine communication, Communication within mines
Very low frequency	VLF	4	3–30 kHz 100 km – 10 km	Navigation, time signals, submarine communication, wireless heart rate monitors, geophysics
Low frequency	LF	5	30–300 kHz 10 km – 1 km	Navigation, time signals, AM longwave broadcasting (Europe and parts of Asia), RFID, amateur radio
Medium frequency	MF	6	300–3000 kHz 1 km – 100 m	AM (medium-wave) broadcasts, amateur radio, avalanche beacons
High frequency	HF	7	3–30 MHz 100 m – 10 m	Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, Over-the-horizon radar, Automatic link establishment (ALE) / Near Vertical Incidence Skywave (NVIS) radio communications, Marine and mobile radio telephony
Very high frequency	VHF	8	30–300 MHz 10 m – 1 m	FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications. Land Mobile and Maritime Mobile communications, amateur radio, weather radio
Ultra high frequency	UHF	9	300–3000 MHz 1 m – 100 mm	Television broadcasts, microwave ovens, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as Land Mobile, FRS and GMRS radios, amateur radio
Super high frequency	SHF	10	3–30 GHz 100 mm – 10 mm	radio astronomy, microwave devices/communications, wireless LAN, most modern radars, communications satellites, satellite television broadcasting, DBS, amateur radio
Extremely high frequency	EHF	11	30–300 GHz 10 mm – 1 mm	radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner
Terahertz or Tremendously high frequency	THz or THF	12	300–3,000 GHz 1 mm – 100 μm	Terahertz imaging – a potential replacement for X-rays in some medical applications, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications, sub-mm remote sensing, amateur radio

ITU

The ITU radio bands are designations defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table^[2]".
The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B.C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. (For example, the approximate geometric mean of Band 7 is 10 MHz, or 10⁷ Hz.)^[3]

Table of ITU Radio Bands

Band Number	Symbols	Frequency Range	Wavelength Range†
4	VLF	3 to 30 kHz	10 to 100 km
5	LF	30 to 300 kHz	1 to 10 km
6	MF	300 to 3000 kHz	100 to 1000 m
7	HF	3 to 30 MHz	10 to 100 m
8	VHF	30 to 300 MHz	1 to 10 m
9	UHF	300 to 3000 MHz	10 to 100 cm
10	SHF	3 to 30 GHz	1 to 10 cm
11	EHF	30 to 300 GHz	1 to 10 mm
12		300 to 3000  GHz	0.1 to 1 mm

† This column does not form part of the table in Provision No. 2.1 of the Radio Regulations

IEEE US Table of IEEE bands[4] Band Frequency range Origin of name [citation needed] HF band 3 to 30 MHz High Frequency VHF band 30 to 300 MHz Very High Frequency UHF band 300 to 1000 MHz Ultra High Frequency L band 1 to 2 GHz Long wave S band 2 to 4 GHz Short wave C band 4 to 8 GHz Compromise between S and X X band 8 to 12 GHz Used in WW II for fire control, X for cross (as in crosshair) Ku band 12 to 18 GHz Kurz-under K band 18 to 27 GHz German Kurz (short) Ka band 27 to 40 GHz Kurz-above V band 40 to 75 GHz W band 75 to 110 GHz W follows V in the alphabet mm band 110 to 300 GHz

EU, NATO, US ECM frequency designations Band Frequency range A band 0 to 0.25 GHz B band 0.25 to 0.5 GHz C band 0.5 to 1.0 GHz D band 1 to 2 GHz E band 2 to 3 GHz F band 3 to 4 GHz G band 4 to 6 GHz H band 6 to 8 GHz I band 8 to 10 GHz J band 10 to 20 GHz K band 20 to 40 GHz L band 40 to 60 GHz M band 60 to 100 GHz

Waveguide frequency bands Band Frequency range [5] R band 1.70 to 2.60 GHz D band 2.20 to 3.30 GHz S band 2.60 to 3.95 GHz E band 3.30 to 4.90 GHz G band 3.95 to 5.85 GHz F band 4.90 to 7.05 GHz C band 5.85 to 8.20 GHz H band 7.05 to 10.10 GHz X band 8.2 to 12.4 GHz Ku band 12.4 to 18.0 GHz K band 15.0 to 26.5 GHz Ka band 26.5 to 40.0 GHz Q band 33 to 50 GHz U band 40 to 60 GHz V band 50 to 75 GHz W band 75 to 110 GHz Y band 325 to 500 GHz

By application

Broadcasting

Broadcast frequencies:

• Longwave AM Radio = 148.5 – 283.5 kHz (LF)
• Mediumwave AM Radio = 530 kHz – 1710 kHz (MF)
• Shortwave AM Radio = 3 MHz – 30 MHz (HF)

Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band. Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned to cellular phone and various land mobile communications systems. Even within the allocation still dedicated to television, TV-band devices use channels without local broadcasters.
The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made obsolete after the introduction of FM broadcasting.