The kinetic isotope effect is a term used in chemistry to describe the difference in reaction rates between identical molecules, where one or more of the atoms are isotopes. Some common synonyms for the phrase include isotopic substitution, kinetic isotopic fractionation, and isotopic discrimination. Isotopic exchange, hydrogen isotope effect, and carbon isotope effect also fall under this umbrella term. The exact terminology may vary depending on the specific application and context, but all describe the phenomenon of isotopes impacting chemical reactions in measurable ways. Understanding these effects is vital in a wide range of fields, including drug development, environmental science, and the study of natural isotopic abundance.