Feature-based modeling refers to the construction of geometries as a combination of form features. The designer specifies features in engineering terms such as holes, slots, or bosses rather than geometric terms such as circles or boxes.
Features can also store nongraphic information as well. This information can be used in activities such as drafting, NC, finite-element analysis, and kinematic analysis. Furthermore, feature-based packages frequently record the geometric construction and modification sequences used in building the model.
Old method: Define slot as Boolean difference between the part and space.
The problem: Lengthening the part geometry turns the slot into a blind hole.
Feature method: Through-hole feature understands that it must pass through the part, no matter how the part changes.