Definition & Meaning of "plumb bob"

What is a "plumb bob"?

A plumb bob is a simple tool used to find a vertical reference line, ensuring that surfaces or structures are perfectly upright. It consists of a weight, usually made of metal, attached to a string or cord. When the plumb bob is suspended from a point and allowed to hang freely, it will align itself with gravity, pointing directly downward. This helps measure or check for vertical alignment in construction, carpentry, and other projects, such as ensuring walls or posts are perfectly straight.