(atmospheric window centered around 2.2 microns, or 136 THz)
The term K band is used in communications as well as astronomy
and refers to different ranges.
For astronomy, it refers to an atmospheric window in the near-infrared
range centered on 2.2 microns (2190nm) or 136 THz,
or a photometric system band aimed at this range,
e.g., with a full width at half maximum of 390nm.
In addition to infrared-specific telescopes,
many optical telescopes can observe in this range.
The letter is also used to indicate the magnitude of the signal
observed through the filter, e.g., citing "K = 1.5".
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European Southern Observatory Very Large Telescope (ESO VLT)
Hawaii K-band Galaxy Survey
Tully-Fisher relation (TFR)