Lightning McQueen competes for the Piston Cup in Pixar's Cars.
The Piston Cup is the fictional stock-car racing championship that drives the first film's plot. Lightning is a rookie contender in a three-way tie for the season lead with veteran racer The King and rival Chick Hicks.
After a highway mishap separates Lightning from his trailer, he ends up in Radiator Springs and is ordered to repair the road. His time in town changes his attitude before the championship race, where his choices matter more than simply taking first place.
The World Grand Prix belongs to Cars 2, while the Florida 500 is the major race in Cars 3. The Piston Cup is therefore the specific championship associated with Lightning's original racing story, not a general name for every competition in the franchise.