Panning is the technique of following and photographing a moving subject with a shutter speed that is slow enough to cause the background to blur but fast enough to capture detail in the subject. Panning is a powerful technique for sports such as race cars, motorcycles, running or bicycling and it works equally well with wildlife. Panning can be used to photograph a bird in flight or a cheetah chasing a gazelle, and is an excellent technique for capturing a feeling of motion and action.
While the technique appears to be easy it requires an understanding of the camera settings and practice. The camera should be set to shutter priority with a shutter speed between 1/15 to 1/30 of a second. I always pan with my camera on a tripod to avoid as much camera shake as possible. Generally small telephotos work well - lenses that have a focal length of 80-150mm, depending upon how close you are to the subject. The aperture setting does not really matter since the background will be blurred, but a wider aperture will create less detail in the background. The aperture can be controlled by adjusting the ISO, a lower ISO setting will allow for a more open aperture.
Panning is not the same as using a fast shutter speed to capture of freeze action such as a bird in flight because this requires a fast shutter speed and often a higher ISO.
If you are interested in learning more about panning and other techniques for photographing movement, please check out my online photography workshop titled Photographing Motion at BetterPhoto.com's digital photography school online.