Energy is a resource that can provide energy. The energy here usually refers to thermal energy, electrical energy, light energy, mechanical energy, chemical energy, etc. Energy sources can be divided into three categories: (1) energy from the sun. Including energy directly from the sun (such as solar photothermal radiation energy) and indirectly from the sun (such as coal, oil, natural gas, oil shale and other combustible minerals and fuels, such as biomass energy, water energy and wind energy). (2) Energy from the Earth itself. One is the geothermal energy stored in the earth, such as geothermal water, underground steam and dry-hot rock mass; the other is the atomic nuclear energy stored in nuclear fuels such as uranium and thorium in the earth's crust. (3) The energy produced by the gravitational pull of celestial bodies such as the moon and the sun on the earth, such as tidal energy. 

The term "energy" was seldom discussed in the past. It was the two oil crises that made it a hot topic for discussion. Today, with the rapid development of the global economy, international energy security has risen to the national level, and all countries have formulated energy policies with energy supply security as the core.

So what is energy? There are about 20 definitions of energy. For example, "Energy is a resource from which energy can be obtained, such as heat, light and power"; Encyclopedia Britannica says, "Energy is a term that includes all fuels, running water, sunshine and wind, and human beings can make it provide the energy they need by appropriate means of conversion"; Encyclopedia Japan "In all kinds of production activities, we use thermal energy, mechanical energy, light energy, electric energy and so on to do work, which can be used as the natural carriers of these energy sources, called energy"; China's "Encyclopedia of Energy" said: "Energy can directly or through conversion to provide the light, heat and movement needed by human beings." Force is the carrier resource of any form of energy. It can be seen that energy is a source of energy in many forms and can be converted to each other. To be exact and simple, energy is a material resource in nature that can provide some form of energy for human beings.

Energy is also called energy resource or energy resource. It refers to the material that can produce various kinds of energy (such as heat, electric energy, light energy, mechanical energy, etc.) or work. It refers to all kinds of resources that can obtain useful energy directly or through processing and conversion, including primary energy such as coal, crude oil, natural gas, coal bed methane, water, nuclear energy, wind energy, solar energy, geothermal energy, biomass energy, secondary energy such as electricity, heat, oil products, and other new energy and renewable possibilities. Source.

energy（Energy Source ）Also known as energy resources or energy resources, is an important material basis of the national economy, the future fate of the country depends on the control of energy. The development and effective utilization of energy resources and per capita consumption are important indicators of production technology and living standards.