Abstract: The Energy Internet has attracted wide attentions, while the understanding and perception of its concept and characteristics are varied at present. To explore the connotations of the Energy Internet and effectively support its substantial advancement, this paper analyzes the development process of the Energy Internet, which can be roughly divided into three stages, including conceptual inoculation and proposing stage, system structure and function research stage, and substantial promotion stage. In addition, the basic connotation of the Energy Internet is analyzed from three perspectives from which the Energy Internet comes, including the ideas of Internet, big power grid, and multiple energy utilizations. Then the definition of Energy Internet is given, i.e., the Energy Internet is a new type of ecological energy system that profoundly fuses the idea and technology of Internet, and the production, transmission, storage and consumption of energy, as well as the energy market. Finally, the characteristics of the Energy Internet are identified from both architecture and category perspectives. From the architecture point of view, the Energy Internet has a four-tier structure:physical foundation, means of realization, value realization and institutional guarantee. From the category perspective, the Energy Internet has two types:energy infrastructure with Internet form, and energy service with Internet form.

Key words: Energy Internet, ecological energy system, energy local area network, energy wide area network, energy world-wide web