In GD&T, profile tolerance defines a uniform boundary around a surface within which the elements of the surface must lie. Profile is a complex tolerance that simultaneously controls a feature's form, size, orientation, and sometimes location. Profile is a three-dimensional tolerance that applies in all directions regardless of the drawing view where the tolerance is specified. It is usually used on parts with complex outer shape and a constant cross-section like extrusions.
An example of profile tolerance is shown below. The top figure shows the profile tolerance applied to a curved surface. The boxed symbols can be read "with respect to datum A, this surface must lie between two surface boundaries 0.8 apart and spaced equally about the true (or ideal) surface profile". The bottom figure shows an example of a part that meets this tolerance.