GD&T stands for geometric dimensioning and tolerancing which is a system for defining and communicating engineering tolerances. In other words, is a set of rules and symbols used on engineering drawings to communicate the intent of a design, focusing on the function of the part.

Using GD&T results in important cost savings during manufacturing phases because only the relevant dimensions or features to the function of the part will be controlled. Thus, the less important dimensions or features can be manufactured with loosened tolerances.