Backmarker
A backmarker is a car at the rear of the field, usually one about to be lapped by the leaders.
Also called lapped car
Being lapped is not a judgement on the driver so much as on the gap between the quickest and slowest cars, which at some circuits is enough to cost a lap inside twenty.
Once shown blue flags a backmarker must let the leaders through. Traffic is a real strategic factor: catching a train of them at the wrong moment can cost more time than a pit stop.