The pitch of the orbiter is a rotation around a defined axis which is through the center of mass of the orbiter from one wing through the other as displayed in the illustration below.

The Quicktime object movie below illustrates the motion around the pitch axis. The orbiter is shown from two perspectives. The perspective on the left shows the shuttle orbiter with the pitch axis horizontal through the center of mass. The perspective on the right shows the orbiter with the pitch axis coming out perpenducular from the screen. Observe the pitch rotational motion of the orbiter by clicking and draging across the picture below.