The document discusses the use of ontologies in ubiquitous computing. It defines what an ontology is and describes ontology languages. It then presents a taxonomy for classifying ontologies used in ubiquitous computing into two main categories: ontologies of the ubiquitous computing domain and ontologies as software artifacts. Examples are given for each category including generic and specific domain ontologies as well as ontology-driven, ontology-aware, and ontology use at development time applications. The conclusion states that many works propose using ontologies in ubiquitous computing and the presented taxonomy can help organize these works.