Solid fuel is a type of fuel that is typically used in furnaces, stoves, and other heating appliances. However, there are several other synonyms for solid fuel, each referring to a specific type of fuel. For instance, coal is one common type of solid fuel, while wood, peat, and charcoal are other types that can be burned to produce heat. Additionally, some solid waste materials, such as plastic, tires, and agricultural waste, can also be used as solid fuels. In some cases, solid fuel may also be referred to as biomass fuel, as it often comes from organic matter that can be used to generate energy.