This subsection provides a concise definition of key terms that are widely used in NMR spectroscopy. The definitions take into account the physical basis of NMR (the mathematical definitions are intentionally set aside), accepted analytical terminology, as well as the historic development and usage of the terms. Defining these terms is independent of the extent of the mathematical, physical, chemical, or biological interpretation that the NMR spectra are supposed to provide. Thus, the terms are equally important to all practitioners of NMR spectroscopy, including those that use NMR spectroscopy as part of a multi-disciplinary experimental design.