Focus and recompose
From The Glossary of Digital Photography
A photographic technique in which the desired focus point is off-center in the scene. The photographer shifts the center of the viewfinder and activates the automatic focus of the camera. Then, by holding the focus lock button, which is often done by holding the shutter release down halfway, the camera is shifted back to the desired composition. In theory this technique should work, but in actual practice it often produces an out-of-focus subject. This problem occurs because most lenses are designed to produce a sharp image of a plane that goes through the center point of the scene. Thus the edges in an image are actually farther from the camera than the center is, yet they are in focus. When the camera view is shifted, the distance to the off-center subject is now shifted and the focus point is different. This is especially noticeable when large apertures (small f-stops) are used.
