In calls for transition to a society in which energy production is based on renewable sources, a fundamental role is increasingly assigned to so-called 'energy communities'. The term 'energy communities' is, however, used to denote a range of different circumstances thus risking overly simplifying the phenomenon. The intention of this article is to discuss what these communities really are or could be. The article is structured into five sections. The first section introduces the main topic. The second section clarifies the use of the term community, and propose an energy community taxonomy (we consider two pairs of options which generate a four-cell matrix: a first distinction can be made between "place-based" and "non-place-based" communities on the basis of a potential correspondence between the community and a specific area; a further difference is that between communities which take shape solely for energy purposes and those with a range of objectives including goals encompassing shared management of energy systems - in this sense, we can distinguish between "single-purpose" and "multi-purpose" communities). The third section considers certain examples which test and exemplify this taxonomy. The fourth section discusses the most significant features which have emerged and considers the main implications (e.g. policy implications). The fifth section concludes by encouraging further critical debate.