What is a Flex Fuel Vehicle? It's a car or truck capable of burning alternative fuels. We're talking about gas engines that can also burn ethanol, natural gas, propane, hydrogen, methanol, and p-series fuels.
Ethanol is alcohol-based and is made by fermenting and distilling corn, barley, or wheat. It can also be made from "cellulosic biomass", such as chunks of trees and grass, except that this version is called "Bioethanol" instead of plain "Ethanol".
E85 is an Ethanol/Gasoline product that's being sold at a lot of gas stations. It's a blend of 85% ethanol and 15% gasoline.
Some service stations are selling an E10 (10/90 ethanol/gasoline blend) and it can be burned by most any engine that burns gasoline.
Unlike Hybrid Vehicles, flex fuel vehicles are not necessarily more expensive because of the alternative fuel option, and they aren't anywhere near as rare.