Avgas (aviation gasoline, also known as aviation spirit in the UK) is an aviation fuel used to power piston-engine aircraft. Avgas is distinguished from mogas (motor gasoline), which is the everyday gasoline used in cars and some non-commercial light aircraft. Unlike mogas, avgas contains tetraethyl lead (TEL), a toxic substance used to enhance combustion stability.
Avgas is used in aircraft that have piston or Wankel engines. Gas turbines are able to operate on avgas, as the pioneering German Jumo 004 turbojet of WWII was able to do, but typically do not, partially for reasons of fuel economy. Turbine and Diesel engines are designed to use kerosene-based jet fuel.
Read more about Avgas: Avgas Properties and Varieties, Avgas Compared To Other Fuels, Environmental Regulation, Phase-out of Leaded Aviation Gasolines, Other Uses