Ambient computing and Internet of Things have reached a level of maturity and a dynamic activity of research and engineering actors. Their goal is to create interactions between a set of distributed devices in an environment, in order to assist human activities. Multi- agent system is an interesting tool for coordinating devices and services for this purpose, because of its adaptation, autonomy and decentralized specifications. However, it is sometimes di cult to understand and share the same idea when it comes to terms such as "Ubiquitous Computing," "Ambient Computing" or the "Internet of Things." As a result, it can be really di cult to browse the literature through research engines and to make a bibliographical study without missing important papers. That is why we want to address this  rst problem by means of a glossary proposal, synthesizing and unifying the extensively cited definitions of the lexicon belonging to these domains. After this necessary step of clarification, we present usability and interest of multi-agent approach in the service of ubiquitous computing.