Tilt-shift photography takes advantage of two aspects of movement: rotation of the lens relative to the image plane (tilt) and movement of the lens parallel to the image plane (shift). Often times special lenses are used with the camera to achieve the effect.
A popular application for tilt-shift photography is tilt-shift miniature faking. This is when the angle of a tilt-shift lens is manipulated in an effort to distort the depth of field of the image. By doing this, a scene may appear smaller than it truly is and appear as though it was fake or a miniature model of the scene.