A wheel with a negative camber angle
Camber angle is the angle made by the wheel of an automobile; specifically, it is the angle between the vertical axis of the wheel and the vertical axis of the vehicle when viewed from the front or rear. It is used in the design of steering and suspension. If the top of the wheel is further out than the bottom (that is, away from the axle), it is called positive camber, if the bottom of the wheel is further out than the top, it is called negative camber.
Camber angle alters the handling qualities of a particular suspension design - in particular, negative camber improves grip when cornering. This is because it presents the tyre which is taking the greatest proportion of the cornering forces at a more optimal angle to the road, increasing its contact area and transmitting the forces through the vertical plane of the tyre, rather than through a shear force across it.