Pan Focus refers to where everything in an image, from the foreground to the background, is in focus.
As a technique, it refers to how a photographer would set a sufficiently wide depth of field to make sure foreground as well as background objects are in focus. A good example here would be landscapes.
As a product, or technology, it refers to how a lens has been designed to be permanently in-focus, with a very wide depth of field. This is in contrast to focusing lens, which is able to isolate a specific subject within a scene.