Dictionary:

backset

  (băk'sĕt')

1. A setback or reversal.
2. An eddy or countercurrent in water.

noun

A change from better to worse: reversal, reverse, setback. See better/worse.

1. The horizontal distance from the face of a lock or latch to the center of the keyhole, knob, or lock cylinder.
2. Same as setback.