The term K Band is used in communications as well as astronomy and refers to different ranges. For astronomy, it refers to a Photometric System Passband centered on 2.2 microns (2190nm) or 136 THz within the Near-infrared range, with a Full Width At Half Maximum of 390nm.
European Southern Observatory Very Large Telescope (ESO VLT)
Hawaii K-Band Galaxy Survey
Tully-Fisher Relation (TFR)