protrusion

A protrusion is any outward extension beyond the surrounding surface or boundary of a structure. It can be a natural anatomical feature, a structural element added in design, or a defect created during manufacturing. The degree of protrusion is often described by height or length relative to the base surface and by the area of contact with the surrounding geometry.

In biology and medicine, protrusions occur at multiple scales. Cells form protrusions such as filopodia and lamellipodia that extend membranes for movement or sensing their environment. In anatomy, bones and soft tissues may have projections or outgrowths, such as bone processes or cartilaginous projections, that create palpable or visible prominences. In geology and geomorphology, rock outcrops or hillocks can be described as protrusions that rise above adjacent terrain.

In engineering and manufacturing, protrusions can be intentional features—such as knobs, fins, or ribs that provide grip, guidance, or heat transfer—or undesired features known as flash or burrs, which may require trimming or deburring to meet specifications. In quality control, protrusions are evaluated against tolerances to determine if they are acceptable or indicate a defect.