Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating
engineering tolerances. It uses a symbolic language on
engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal
geometry and its allowable variation. It tells the manufacturing staff and machines what degree of
accuracy and precision is needed on each controlled feature of the part.. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features..