A variety of methods and techniques have been developed to assess the usability of web-based user interfaces of information systems. Even though language-related questions have been considered in the literature of user interface design and usability, we find that usability and the theory of terminology have evolved independently from each other. Despite this fact, these two areas of research have the potential to be mutually beneficial. Within the context of the theory of terminology and usability, this paper discusses how the theory of terminology can be applied to promote usability. We will concentrate on one aspect, appropriateness, which is the basis for every usable system. Appropriateness means that a system or a product is suitable for its purpose. It also includes the idea that terminology used is appropriate for the specified users (the persons for whom the system has been designed) and for the context (the situation and tasks for which it is used). This paper is part of an ongoing research project that focuses on the usability of information systems from a terminological perspective.