A cutting point is an empty point between two chains of stones. If the opponent plays at that point, the two chains are cut.
If the cutting stone can be captured immediately, there is no cutting point.
It is important to defend your cutting points.
In this diagram, the marked black stone protects the cutting point in a fancy way (see keima protecting the cutting point). If White cuts, her cutting stone will be captured in a ladder towards the bottom, or in a loose ladder towards the left. So in a broader sense, there is no cutting point, yet this position still contains some aji.