This is a lens that’s designed to be as slim as possible so that the camera/lens combination is lighter, more compact and more unobtrusive. Pancake lenses are usually fixed focal length, or ‘prime’ lenses, but it’s possible to get a few pancake zooms too. Making a lens this small does bring compromises. With prime lenses it usually means a smaller maximum aperture and with zooms in may need a more complicated retracting mechanism or electrical ‘power zoom’ which also retracts the lens when the camera is switched off.