Solid fuel refers to any fuel that is in a solid state, commonly used for energy production. Examples include coal, wood, and pellets. These fuels are burned to release energy, which can be used for heating, electricity generation, or powering vehicles. Solid fuels are often favored for their availability and cost-effectiveness. They can be sourced from natural materials or manufactured products, such as briquettes. However, burning solid fuels can produce emissions, which may impact air quality and contribute to environmental concerns.