A setback or reversal of progress, or in carpentry, the recessed area on a door frame where the door actually closes.
Compound of 'back' and 'set' (Old English 'settan'). The carpentry meaning refers to where the door 'sets back' into the frame.
In carpentry, understanding backset measurements is critical because a door frame with the wrong backset won't close properly—it's such a small detail (usually ½ to ¾ inch) that it's easy to overlook, but it makes the difference between a smooth-closing door and one that binds.
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