Since the dawn of civilization, humans have used solid biofuels for heat and cooking (solid biofuels in the form of firewood/fuelwood have been in use since the dawn of civilization). Biofuels can be made from wood, sawdust, or leaves. Solid biofuels are organic, non-fossil materials of biological origin (often referred to as biomass) that can be utilized as a source of heat or energy. Because many people identify biofuels with advanced refining and chemical processes, the term "solid biofuel" can be deceptive. Biofuels can be any renewable, biological material that is used as a source of energy. Solid biofuels are defined as a product aggregate consisting of fuelwood, charcoal, wood residues and by-products, black liquor, bagasse, animal waste, other vegetal materials and residuals, and the renewable fraction of industrial waste, according to energy data.