1. In nearshore, shoaling waters, each particle-size of sediment should hypothetically have a null point, where there is no net movement of the particle landward or seaward. It is the point where there is a balance between the component of gravity acting down the slope in a seaward direction and the force on the particle resulting from the difference between the crest and trough velocities of the waves which tends to move the particle landwards.

2. In an estuary, the point at which the residual sea water landward flow is balanced by the seaward residual river flow.