This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
Although the railroad term switchback arises from early mountain
railroading where at the end of a traverse, a switch is turned to back
up the next traverse, after which another switch is turned to head up
the next, on roads these are hairpin turns. In such turns trajectory
asymmetry is most conspicuous, because braking can be hard enough to
raise the rear wheel when entering but one cannot exit with such
acceleration. For this reason, riders often find themselves with
extra road on the exit of such turns, having slowed down too much.