The pull force is the force required to pull a magnet directly off of a steel plate. As it is measured in laboratory conditions, most real world applications will not reach the maximum pull strength listed.
Pull Force is measured in pounds or kilograms.
Many factors can impact why the magnet may not be performing at the listed pull strength. Most commonly it is due to gravity. The strength of the magnet drops 65% or more when used in a horizontal application such as on the side of a refrigerator instead of in a vertical application such as on the underside of a metal beam. Other factors such as the composition and thickness of the metal being used will also impact performance.