Energy is the capacity of a system or substance to do work. It is a fundamental concept in physics and is essential for all forms of life on Earth. Energy can exist in many forms, such as kinetic energy (energy of motion), potential energy (stored energy), thermal energy (heat), chemical energy (energy stored in chemical bonds), electrical energy, and more.
In the context of society, energy is primarily used for power generation, transportation, and industrial processes. The most common sources of energy used today are fossil fuels (such as coal, oil, and natural gas), nuclear power, and renewable energy sources (such as solar, wind, hydro, and geothermal).