The Autofocus Lock (AF Lock) is possibly one of the most useful additions to camera technology since, well, autofocus. AF Lock allows you to focus on a subject and then reposition your camera in order to reframe the shot. The use of Auto Focus Lock is fairly simple. As always, you would center your subject within the focus area and press your shutter button half-way. Autofocus will then determine an appropriate focus. On most cameras, you then press-and-hold the AF Lock button and reposition your camera.
This is especially beneficial to those with consumer-level cameras that have fewer autofocus zones. While higher-end cameras may provide more focus zones, the use of AF Lock will basically take the focus zone count out of your criteria when choosing a camera.