Perspective Control Lens or Tilt Shift Lens allows the photographer to change the perspective in the photo without moving the camera body itself.
Tilt means that lens plane is tilted relative to the image plane (sensor/film), so that the plane of focus is at an angle to the image plane, and objects at different distances from the camera can all be sharply focused if they lie in the same plane.
Shift means that the lens can be moved parallel to the sensor or the film. It's often used to avoid convergence of parallel lines, such as when photographing a skyscraper or tall buildings.
