With the growth in the number International Standards that directly or indirectly relate to energy, there is an increasing need for an agreement on a common language in the domain. The aim of this document is to support activities related to energy and energy efficiency. This standard is a horizontal standard in accordance with IEC Guide 108, which includes the fundamental principles and concepts of energy efficiency and energy management terminology. Since these are addressed or relevant in a number of technical committees, the purpose of this document is to improve coherence and highlight common characteristics for energy terms. The document does not address terms specific to topics such as environmental sustainability or nuclear energy. It is intended for technical practitioners and other interested parties who either use or develop International Standards in this subject area. This part contains transversal concepts and their definitions from the subject area of energy efficiency. The responsible national standardization committee is Working Committee NA 172-00-09 AA "Energieeffizienz und Energiemanagement" ("Energy efficiency and energy management") at DIN Standards Committee Principles of Environmental Protection (NAGUS).