ASME Y14.5 : Dimensioning and Tolerancing
A physical portion of a part (such as a surface, pin outside diameter, hole, or slot) or its representation on drawings, models, or digital data files.
See Also:
Part, Drawing, Model
Alternate Definitions:

MIL-STD-31000B - A feature is a portion of an object defined by a procedure and controlled by parameters. Changing the parameters changes the feature dimensions. Examples of features include round holes, arbitrary cutouts, extrusions, volumes of revolution, sweeps, and lofts.

PTC - Any self-contained set of elements that can be defined and stored with the model and which has an impact on the geometry. A feature can be physical (hole, draft), procedural (for example, machining strategy in Expert Machinist), or computational (analysis). Features are listed on the Model Tree.