Tilt-shift photography refers to the use of camera movements on small- and medium format cameras. In many cases, it refers to tilting the lens relative to the image plane and using a large aperture to achieve a very shallow depth of field. The technique relies on the Scheimpflug principle and usually requires the use of special lenses.
“Tilt-shift” actually encompasses two different types of movements: rotation of the lens, called tilt, and movement of the lens parallel to the image plane, called shift. Tilt is used to control the orientation of the plane of focus (PoF), and hence the part of an image that appears sharp. Shift is used to control perspective, usually involving the convergence of parallel lines.