K band

Within astronomy, the term K band refers to an atmospheric window within the near-infrared range centered on 2.2 microns (2190 nm) or 136 THz, and a photometric system band aimed at this range, e.g., with a full width at half maximum of 390 nm. 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".

The term K band also has other meanings outside astronomy and there are at least two K bands defined for radio communications (nowhere near the above infrared band).