What is the difference between Spot AF and Single-Point AF?

According to the Canon 7D manual on page 89, “Although this is the same as single-point AF, the selected AF point covers a smaller pinpoint area to focus. Effective for pinpoint focusing of overlapping subjects such as an animal in a cage. Since Spot AF covers a very small area, focusing might be difficult during hand-held shooting or for a moving subject.”

Basically Spot AF covers a smaller area than single-point AF. Many photographers use Spot AF to focus on the eye of a person or animal to get as sharp an image as possible. Spot AF is also used to focus on the most important part of a complex object that must be “critically” sharp.