In Information Systems, enterprise modelling has been a pivotal field of research that has evolved over a period of more than 20 years. In recent years, the main research focus was on adapting approaches to enterprise modelling to changing requirements, e.g. provide support for IT management. To develop a better understanding of the motivation, objectives and concepts that are characteristic for enterprise modelling, it is important to study the terminological background. On the one hand, it builds the foundation for the conceptualisation of enterprise models, on the other hand, it helps to clarify the semantic relation of the term enterprise model to terms in its surroundings such as information system, conceptual model etc. This report is aimed at developing conceptualisations of respective terms. Starting with more generic terms like domain, model or information system, the course of the investigation gradually moves forward to conceptual model, action system, and enterprise model. Finally, an elaborate conception of multi-perspective enterprise models is presented that is intended to characteristic aspects of their structure, the intentions related to them and preconditions of their reflective use.