means A sharp, hairpin bend in a road, trail, or railway that doubles back on itself to climb or descend a steep slope at a manageable gradient.

from A plain English compound of "switch" and "back" — and the "switch" here is the railroad sense, the movable rail that throws a train from one track onto another. In 19th-century American mountain railroading, a switchback was a section where a train ran up a slope, the switch was thrown, and it then reversed back up the next incline, climbing in a zigzag rather than tackling the grade head-on. The word soon spread from rails to mountain roads and footpaths that pull the same trick.