Extrude

Extrude is a common operation in 3D modeling where a selected face, edge or profile of a mesh is 'pulled out' to create new geometry. During extrusion the selected element is typically duplicated and connected with new side faces, adding volume or thickness to the model and changing its topology. Extrusion can be performed along the surface normal, a specific axis or along a curve/path, and is used to model features, extend edges, create walls or ribs; care must be taken with normals and edge flow to avoid non-manifold geometry or shading issues.

Imagine creating a building wall in a 3D design: you start from a plane and extrude it upward to form a wall with thickness. When making a game asset you might extrude an eye socket from the head mesh to add depth, then refine the edges and vertices for a smooth transition. For 3D printing, a profile is often extruded along a path to produce a solid part; in that workflow you must ensure the resulting topology is watertight and free of overlapping faces.