Biodiesel is fuel derived from plant or animal matter used in a diesel engine instead of fuel processed from petroleum. For example, used cooking oils from restaurants have been processed to serve as diesel fuel.
Around the 2000s, alternative biofuels, like recycled cooking oils especially, were seen as the future of curbing vehicle emissions, because they burned cleaner than gasoline and regular diesel. Cars, that could run on such biodiesel, became somewhat popular then. Those vehicles have since fallen out of fashion because of the rise and promise of zero-emissions electric vehicles.
