Hairpin
A hairpin is a very tight corner that turns the car through roughly 180 degrees, usually taken in a low gear after heavy braking.
Also called: hairpin bend, U-turn corner
A hairpin doubles the track back on itself. It typically follows a straight, so it is a heavy braking zone, and it is taken at the slowest speed on the lap. Because it leads onto another straight, the exit is almost always worth more than the entry.
The standard approach is to brake in a straight line, trail off the brake as you turn in, and use a late apex so the car is pointed down the exit before you go to full throttle. Many hairpins reward a slightly wider entry to open the radius. Be patient: the time is made when you can go to throttle early and keep it there.
Common errors are braking too late and sliding past the apex, turning in early and running out of room on exit, or flooring a powerful car too soon and spinning the inside rear. In a rear-drive car, squeeze the throttle progressively as you unwind the wheel.
Hairpins lead onto straights, so a patient, late-apex hairpin is often one of the biggest single sources of lap time.