What is the focus limiter?

What is the focus limiter? How and when should it be used?

Thank you.

With some lenses, primarily macros or long telephotos, the amount of focusing movement between infinity and the closest focus can be quite large. If a lens used all of the focusing range it could work quite hard, so a focusing limiter will confine the focusing range as indicated on a dial on the lens. This will make focusing over a smaller range of distances quicker and less of a load on the focusing system.