The ESPEN guidelines on enteral nutrition are the first evidence-based European recommendations for enteral nutrition. They were established by European experts for a variety of disease groups. During guideline development it became evident that terms and definitions in clinical nutrition have been used inconsistently depending on medical disciplines as well as regional and personal preferences. Therefore, to increase explanatory accuracy it was necessary to unify them. In this chapter terms and definitions used throughout all guidelines are explained. Additionally answers to more general questions, which might be important in most indications are dealt with, i.e. use of fibre containing and diabetes formulae.