Nomenclature (UK: , US: ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally agreed principles, rules and recommendations that govern the formation and use of the specialist terminology used in scientific and any other disciplines.

Naming "things" is a part of general human communication using words and language: it is an aspect of everyday taxonomy as people distinguish the objects of their experience, together with their similarities and differences, which observers identify, name and classify. The use of names, as the many different kinds of nouns embedded in different languages, connects nomenclature to theoretical linguistics, while the way humans mentally structure the world in relation to word meanings and experience relates to the philosophy of language.

Onomastics, the study of proper names and their origins, includes: anthroponymy (concerned with human names, including personal names, surnames and nicknames); toponymy (the study of place names); and etymology (the derivation, history and use of names) as revealed through comparative and descriptive linguistics.

The scientific need for simple, stable and internationally accepted systems for naming objects of the natural world has generated many formal nomenclatural systems. Probably the best known of these nomenclatural systems are the five codes of biological nomenclature that govern the Latinized scientific names of organisms.