This chapter aims to provide more accessible definitions for terms that are used in the networks and energy transition related activities. This chapter is intended to be a reference for stakeholders to provide clarity when discussing the use of the distribution and transmission networks in Great Britain and not as definitive industry definitions. It includes description for many of the terms that are being used in areas such as the connection of resources to distribution networks and the provision of services from Distributed Energy Resources (DER) to support transmission and distribution network operation.