International Union of Pure and Applied Chemistry. An international nongovernmental body formed in 1919 to foster worldwide communications in chemical science, both academic and industrial. IUPAC is the international authority defining recommended terminology, atomic weights, isotopic abundances, and other data. The IUPAC rules for systematic chemical nomenclature are widely adopted. IUPAC also introduced the InChI line notation for compounds.

https://www.iupac.org/ The IUPAC home page