A traditional Petroleum Diesel equivalent made from plant and animal oil sources. Frequently made from Soy, Canola, and other commerical vegetable oils. Can be made from waste oil as well.

I don't completely remember the science, but you take oils, you start with triglycerides, and through transesterification – mixing with alcohol in some steps – end up with long-chain fatty acid esters; this is the biodiesel... and glycerin as the "waste"? something like that...