In radio, a continuous sequence of broadcasting frequencies within given limits.

In radiometry, a relatively narrow region of the electromagnetic spectrum to which a remote sensor responds; a multispectral sensor makes measurements in a number of spectral bands.

In spectroscopy, spectral regions where atmospheric gases absorb (and emit) radiation, e.g., the 15 µm carbon dioxide absorption band, the 6.3 µm water vapor absorption band, and the 9.6 µm ozone absorption band. 
NASA Earth Observatory