Terminology is assigned to play a more and more important role in the Information Society. The need for a computational representation of terminology for IT applications raises new challenges for terminology. Ontology appears to be one of the most suitable solutions for such an issue. But an ontology is not a terminology as well as a terminology is not an ontology. Terminology, especially for technical domains, relies on two different semiotic systems: the linguistic one, which is directly linked to the " Language for Special Purposes " and the conceptual system that describes the domain knowledge. These two systems must be both separated and linked. The new paradigm of ontoterminology, i.e. a terminology whose conceptual system is a formal ontology, emphasizes the difference between the linguistic and conceptual dimensions of terminology while unifying them. A double semantic triangle is introduced in order to link terms (signifiers) to concept names on a first hand and meanings (signified) to concepts on the other hand. Such an approach allows two kinds of definition to be introduced. The definition of terms written in natural language is considered as a linguistic explanation while the definition of concepts written in a formal language is viewed as a formal specification that allows operationalization of terminology.