distortion
deviation from rectilinear projection (optics)
barrel distortion
image distortion in photographs caused by inherent imperfections in the camera/lens optical system, resulting in an image where straight lines appear slightly bent, stronger near image borders, such that square objects appear rounded or "bloated"
pincushion distortion
image distortion in photographs wherein square objects appear to have an outer shape like a pillow; due to imperfections in the camera/lens system, resulting in an image where straight lines appear slightly bent which is stronger near image borders