The state of a structural element being exactly vertical, typically checked using a spirit level or a weighted string line. It is the vertical equivalent of being level. Framing walls, setting doors, and laying masonry all require strict adherence to this alignment to ensure structural stability and proper fit of subsequent materials.
Heard on the job
Check that corner post with the six-foot level to make sure it's dead plumb before you brace it.
Insider tip
A wall that is out of plumb will cause doors to swing open on their own and make drywall installation difficult.