https://doi.org/10.1351/goldbook.G02705
A defined linked collection of atoms or a single atom within a molecular entity. This use of the term in physical organic and general chemistry is less restrictive than the definition adopted for the purpose of nomenclature of organic compounds.
See also: characteristic group (in organic nomenclature), principal group (in inorganic nomenclature) (in organic nomenclature), substituent (in organic nomenclature)