Curvilinear distortion is a lens aberration that combines elements of both barrel distortion and pincushion distortion. In this type of distortion, straight lines in the subject may appear curved, either bulging outward (barrel) or pinching inward (pincushion), depending on the lens design and focal length. Curvilinear distortion is commonly observed in wide-angle and zoom lenses and can affect architectural and product photography where straight lines are critical. It can be corrected using software in post-processing or minimized through careful lens selection and shooting technique.