A spectrum is the arrangement of a frequency- or intensity distribution as a function of certain tagged values. In a narrow sense one understands as spectrum the representation of the intensity distribution of an electromagnetic radiation in dependence on its frequency, wavelength, or wavenumber.
Spectrometry, a distinction is made according to the range of the electromagnetic spectrum into radio waves (NMR), microwaves, infrared, UV-VIS, X-ray and gamma-ray spectrometry, according to the type of interaction in absorption, emission, reflection and scattering spectrometry as well as by the type of sample examined in atomic, molecular or solid-state spectrometry.
Mainly spectrometry is used for the identification of substances. It provides information on the structural configuration and the qualitative composition of the systems investigated. Quantitative statements about the quantitative composition of the samples is obtained from the intensity of radiation at a wavelength, but spectrometers needs to be calibrated.