In Computer-Aided Design (CAD), a feature refers to a specific geometric shape or attribute of a model, such as holes, fillets, chamfers, or extrusions. Features are the building blocks of a CAD model, representing the individual design elements that make up the overall shape and form of the object being designed.

Features are typically created by applying specific modeling operations to a base geometry, such as a sketch or a previous feature. Some common types of features in CAD include:

1. Extrude: A feature that creates a 3D shape by extending a 2D profile along a straight path. Extrusions are commonly used to create basic shapes like boxes, cylinders, and prisms.

2. Revolve: A feature that creates a 3D shape by rotating a 2D profile around an axis. Revolves are commonly used to create cylindrical or axisymmetric shapes like shafts, bottles, or bowls.

3. Sweep: A feature that creates a 3D shape by moving a 2D profile along a defined path. Sweeps are commonly used to create complex or organic shapes like tubes, pipes, or moldings.

4. Loft: A feature that creates a 3D shape by interpolating between two or more 2D profiles. Lofts are commonly used to create smooth, transitional shapes like airplane wings, car bodies, or ergonomic handles.

5. Fillet: A feature that rounds the sharp edges or corners of a model, creating a smooth transition between faces. Fillets are commonly used for aesthetic or ergonomic purposes, or to reduce stress concentrations.

6. Chamfer: A feature that creates a beveled or angled edge on a model, typically at a 45-degree angle. Chamfers are commonly used for aesthetic or manufacturing purposes, such as creating a lead-in for a mating part.

Features are an essential concept in parametric modeling, where the geometry of a model is defined by parameters and relationships. By creating and combining features, designers can build up complex models from simple sketches and extrusions, and can easily modify and update the model by changing the parameters and constraints that define each feature.

Most CAD software packages provide a wide range of tools and features for creating and editing features, including sketch-based features, feature-based modeling, and direct editing tools. These tools allow designers to quickly and easily create and modify features, and to explore different design variations and iterations.