What do we refer to as materials that store energy?

Materials that store energy are referred to as fuels. Fuels are substances that can release energy when they undergo a chemical reaction, typically through combustion. This energy release is what makes fuels essential for various applications, including heating, powering engines, and generating electricity. Fuels can include a wide variety of materials, such as hydrocarbons (like gasoline, diesel, and natural gas), wood, coal, and even some metals.

Elements, while fundamental substances consisting of one type of atom, do not inherently refer to materials that store energy since many elements do not provide energy on their own in a usable form. Conductors and insulators are terms associated with the transfer of electricity and heat, rather than energy storage. Conductors allow energy to flow freely, while insulators resist the flow of energy, so they are not directly related to the concept of storing energy in the same context as fuels.