a car that drives so slow in a race that it just slows the other cars as they have to pass by it and doesn't really compete. In a race, it usually ends several laps behind the winner. See Minardi.
The Minardi cars ended the race 4 laps behind Fernado Alonso.
Multiplayer race winner: That n00b was 5 laps behind me!
Other driver: Yeah, he was just a mobile chicane. Slowing us down!