The Energy Systems . Terms and definitions. GOST 21027-75”, created by the team of authors, is an indispensable guide for specialists in the field of energy, engineers and students of technical universities This publication not only systematizes the most important terms and definitions, but also serves as a basis for understanding the complex processes associated with energy systems. Energy is one of the key sectors that determine the development of modern society. With rapid progress and constant changes in technology, knowledge of the basics and terminology becomes necessary for successful work in this area. The book offers readers clear and concise definitions, which makes it easy to navigate complex concepts and terms that may arise in the process of work or learning. This book will be interesting not only for professional power engineers, but also for students who are just starting their way in this field. It will become a reliable assistant for those who study such disciplines as electrical engineering, thermal power engineering, as well as for those who want to better understand the principles of operation of various energy systems. Readers interested in modern technology, sustainable development and the environmental aspects of energy will also find a lot of useful information in it. The topics raised in the book cover a wide range of issues related to energy systems. It examines the main types of energy resources, their classification, as well as the principles of operation of various systems, from traditional to renewable energy sources. The book focuses on the importance of proper understanding of terminology for effective interaction between specialists in different fields, which is especially relevant in the context of globalization and an interdisciplinary approach to solving energy problems. The style of the authors is distinguished by clarity and accessibility, which makes the material understandable even for those who are just beginning to get acquainted with this complex topic. The book is written taking into account current standards and norms, which emphasizes its practical value. It can serve not only as a training manual, but also as a reference material for professionals working in the field of design, operation and management of energy systems. In addition, "Energy Systems. Terms and definitions. GOST 21027-75" can be useful for scientists and researchers engaged in the development of new technologies and methods in the field of energy. This publication will help them better understand existing standards and requirements, which in turn can contribute to the creation of more effective and secure solutions. In conclusion, the book “Energy Systems . Terms and definitions. GOST 21027-75 is not just a collection of terms, but an important resource for anyone who wants to understand the world of energy more deeply. It combines theoretical knowledge and practical aspects, making it an indispensable tool for studying and working in this dynamically developing field. If you are looking for professional growth or want to expand your knowledge in the energy sector, this publication will become your reliable companion along the way.