Targan is spot on - Biodiesel is, loosely speaking, diesel fuel produced by recycling used vegetable oils (from restaurant fryers, potato crisp makers etc) or by using treated rape seed or palm oil. Biogas is the production of methane from biological waste materials including animal poo.
http://en.wikipedia.org/wiki/Biodiesel
http://en.wikipedia.org/wiki/Vegetable_oil_used_as_fuel
http://en.wikipedia.org/wiki/Bioconv..._alcohol_fuels