(range of electromagnetic wavelengths that a filter allows)
A passband (or just band) is a specification of the range and strength
of wavelengths (and in effect, frequencies)
allowed through a filter that cuts off both high and low wavelengths,
i.e., a specification of the wavelengths
allowed to pass through the filter.
In effect, it is a sensitivity function.
The term is also used to mean the filter itself.
Filter and passband are common terms in optical-like telescopes
(infrared through ultraviolet) while the word band
is also used in radio astronomy to refer to the wavelength-sensitivity
of a radio receiver and as a general term for a wavelength
or frequency range.
The term is used in engineering disciplines such as communications
engineering as well as astronomy.
In the latter, a photometric system,
e.g., the UBV photometric system,
is a conventional set of such filter specifications.
The passbands/filters are generally indicated by letter,
some being mnemonic for the color, e.g.,
B for Blue, R for Red,
but the same letter may have differing specifications under different systems.
Some common passband letters in astronomy:
The letters Z, Y, J, H, K band, and L are typical of
near infrared, and M, N, and Q of mid infrared.
Atacama Cosmology Telescope (ACT)
Arecibo Observatory (NAIC)
Cherenkov Telescope Array (CTA)
Deep Lens Survey (DLS)
full width at half maximum (FWHM)
gas fraction estimation
Green Bank Telescope (GBT)
globular cluster luminosity function (GCLF)
Gran Telescopio Canarias (GTC)
Hawaii K-band Galaxy Survey
Hubble Ultra-Deep Field (HUDF)
imaging Fourier transform spectroscopy (IFTS)
JHK photometric system (JHK)
Large Binocular Telescope (LBT)
Large Millimeter Telescope (LMT)
luminosity function (LF)
mid infrared (MIR)
NOAO Deep Wide-field Survey (NDWFS)
Ooty Radio Telescope (ORT)
Owens Valley Radio Observatory (OVRO)
Plateau de Bure Interferometer (PdBI)
radio frequency interference (RFI)
Sloan Digital Sky Survey (SDSS)
sensitivity function (S)
Spitzer Space Telescope (SST)
Strömgren photometric system
Subaru XMM-Newton Deep Survey (SXDS)
Two Micron All-sky Survey (2MASS)
UBV photometric system
Very Long Baseline Array (VLBA)
Very Small Array (VSA)
Wide Field Infrared Explorer (WIRE)
Wide-field Infrared Survey Explorer (WISE)