Overhang: An overhang is a part surface that faces downwards beyond the angle a 3D printer can build without support, usually measured from vertical.
Each new layer has to rest partly on the one below it. When a face leans out too far, the new layer has nothing to sit on and sags, curls or fails. For FDM the common rule is that faces up to about 45° from vertical print without support structures; resin and metal processes have their own limits. A bridge, a flat span held up at both ends, can often print unsupported over a short distance.
What it means for the price
Every overhang beyond the limit adds support, and support adds material, machine time and labour. Turning the part can remove overhangs, but it may make the part taller (more layers) or move the support marks onto a face that matters. A DFM check that flags overhangs at quote time helps the buyer see why one design costs more than another, and what to change.
Example: a ledge with a 45° chamfer underneath prints clean; the same ledge with a flat underside needs support along its whole length. The figures are an example.
Common confusions
Some software measures the overhang angle from horizontal rather than vertical, so the same face can be called 30° in one tool and 60° in another. Check which convention a rule uses before applying it. Read design for 3D printing.
Go deeper: Design for 3D printing: walls, overhangs, holes, clearances and orientation