What is a biofuel and why are they often considered carbon neutral?
Biofuels are fuels that are created from plant based feedstocks that can be grown,
Common examples are bioethanol (made by the fermentation of wheat, corn, sugar cane or other suitable crops), and biodiesel (made by chemical reaction of vegetable oil, often rapeseed oil, but also commonly "used cooking oil").
They are not necessarily absolutely carbon neutral but they are a lot more neutral than things like fossil fuels (coal or oil). The reason is that the feedstocks for biofuels are grown as crops, or plants. The process of growing vegetation causes carbon dioxide to be absorbed by the growing crops, which helps to offset (to an extent, anyway) the carbon dioxide that is eventually released by burning the biofuel in car engines.