A system for naming heterocyclic compounds, independently introduced for naming 5- and 6- membered nitrogen monocyclic compounds by Arthur Rudolf Hantzsch (1857–1935) in 1887 and Oskur Widman (1852–1930) in 1888. Subsequently it was extended to other ring sizes and other hetero atoms. It is based on prefixes denoting the hetero atoms(s) (e.g. aza-for nitrogen, thia- for sulphur, oxa- for oxygen), and items denoting ring size and saturation. For example, 4- membered rings have ete for unsaturated rings and etane for saturated; 5- membered rings have ole for unsaturated and olane for saturated compounds. Rules are given for naming compounds with two or more different hetero atoms and for numbering the atoms. The system is widely used both for monocyclic compounds and for heterocyclic components of polycyclic compounds.

https://www.qmul.ac.uk/sbcs/iupac/ Information about IUPAC nomenclature