This chapter provides a structured overview of terminology relevant to distributed energy resources (DER), renewable generation, storage systems, and active distribution networks. It aims to establish a consistent language for engineers, researchers, and practitioners working in the field of modern power systems, where increasing penetration of variable renewable generation and digitalization is reshaping grid operation. The first part introduces distributed and renewable generation technologies, including solar, wind, hydro, geothermal, biomass, and emerging low-temperature thermal systems. It also addresses the role of prosumers, environmental aspects, and generation control requirements. The section highlights the importance of inverters and power electronics as key enabling technologies for DER integration. The second part focuses on demand-side integration, emphasizing consumer participation, demand response, and multi-energy coordination. This is followed by an in-depth treatment of storage systems, with particular attention to battery energy storage systems (BESS), their chemistries, performance metrics, and the growing role of electric vehicles as mobile storage units. The largest section addresses active distribution networks (ADN), describing key concepts, stakeholders, and technical equipment. It explains operational terms such as flexibility, hosting capacity, operating envelopes, and advanced control methods while also examining power quality, security, and reliability aspects. Operational paradigms such as virtual power plants, microgrids, intentional islanding, energy communities, and transactive energy are presented, alongside their relevance for future grid operation and market participation. By consolidating definitions across technologies, stakeholders, and operational models, this terminology guide supports clarity and knowledge transfer in a rapidly evolving energy landscape, enabling consistent communication and more effective system planning, operation, and innovation.