Spectral resolution is the number and dimension (size) of specific wavelength intervals (referred to as bands or channels) in the electromagnetic spectrum to which a remote sensing instrument is sensitive.
Spectral resolution describes the ability of a sensor to define fine wavelength intervals. The narrowest spectral interval that can be resolved by an instrument. Spectral resolution (spectral capability) also refers to the number of wavebands within the EM spectrum that an optical sensor is taking measurements over.