Fryer grease that is no longer suitable for cooking. With heat, fryer grease breaks down the structure of the oil changing its flavor. The oil also becomes contaminated by the compounds from the foods being fried.

Sometimes also referred to as waste vegetable oil or WVO, although strictly speaking, this is an inaccurate use of the terminology.

As small-scale and home-produced biodiesel production has become more popular, waste vegetable oil and restaurant grease has become more sought after. Restaurants and others with WVO have also realized that they have a commodity they may be able to give away, reducing their costs for transportation to a landfill. Websites like NC Biomass Trader have sprung up to connect people looking for WVO and organizations looking to offload this waste product.