A gravel trap is an area of gravel on the side of the track designed to slow cars down rapidly if they leave the track at high speed. Due to the fact that cars can become beached in the gravel trap, they also act as a deterrent to keep cars from going too wide. 

An alternative on F1 grade tracks is a tarmac runoff painted with stripes of high grip compound designed to rapidly slow the car. 

Andrew Burden

The author Kiwi F1 Fan