The purpose of this paper is to offer a reasoned analysis of the diversity of terminology today, looking at three aspects: its definition, the different trends or approaches which contribute to the development of terminology and its numerous and varied applications. The different meanings of the term 'terminology' are considered –as a discipline, as a practice and as the product of that practice. Next, terminology is defined as an object, i.e. as the collection of specialised terms. Finally, the article assesses the evolution of terminology thanks more to the terminological practice than to the theoretical contribution. Based on this analysis, the author concludes that it is necessary to accept the notion of diversity as an essential aspect to typify and delimit terminology, as to both its theoretical definition as a discipline and its application.