A technical term – henceforth simply ‘term’ – is a linguistic sign that represents a concept of a scientific or technical discipline. For instance, significans and signifiant are Latin and French terms, resp., to represent the concept “expression side of a linguistic sign”.

Technical concepts are sometimes precise and general in the sense that they are understood in the same way all over the world. In that case, terms of different languages representing them are not only loose translation equivalents, but fully synonymous. For instance, Latin significans and French signifiant are fully synonymous. As a consequence, a multilingual dictionary is relatively easy to make if it is a terminological dictionary.

While the concepts of ‘sign’ and ‘significans’ are clearly distinct theoretically, they are distinguishable in practice only if they vary independently from each other. Now in a systematic terminology, there is a biunique correspondence between term and concept within each language, and cross-linguistically, terms are fully synoymous. As a consequence, the concepts of ‘significans’ and ‘sign’ here become indistinguishable, and the term ‘term’ is frequently taken not to mean a sign, but a significans of a scientific concept.

The concept designated by a term is independent from that term. That implies that it is not part of a language, but exists in some mental space and may correspond to some extralinguistic reality. Concepts designated by terms are reified in some way. To this corresponds a formal constraint on terms: Not every expression designating a concept is a term; it must be a common noun.

Thus, homonymy, direct object, assimilation are terms. Homonymous and assimilate are not terms because they are no nouns. Edward Sapir is not a term because it does not designate a concept (and is not a common noun).

The terminology of a discipline or field of knowledge is the set of terms relevant to it, conceived as a conceptual system. Since about the end of the twentieth century, it has been fashionable to call a terminology an ‘ontology’; but here it will be called a terminology.