What does holding force mean?

The holding force is normally shown in newtons or kilograms per area. We give it in kilograms or grams per square centimeter.
For the Memo magnets we use an amount of A4 papers that a magnet can hold on a vertical surface. This is easier for you (the customer) in assessing a certain strength.

The holding force is of course dependent on the size, surface (smooth), thickness, degree and direction of the magnet.