Illustrated Glossary of Organic Chemistry

Integral: In NMR spectroscopy, area of an NMR signal as measured by integration. The area corresponds to the amount of energy absorbed or released by all nuclei of a given chemical shift during the nuclear spin flip process, in accordance with Beer's Law. The resulting integrals are used to determine the ratio of hydrogens (or rarely carbons) that correspond to the signal.

The 1H-NMR spectrum of CH3OCH2Cl shows two signals:
5.46 ppm (singlet; integral = 1.0) corresponds to the CH2 group.
3.51 ppm (singlet; integral = 1.5) corresponds to the CH3 group.