The Probability Density Function(PDF) is a graphical function that shows the probability of a certain event being above or below the graph. Such a graph represents only a threshold, for the probability statement.
A typical example is the Gaussian distribution curve. If one enters the events to be evaluated into the coordinate system with the distribution curve, then quite a few events lie above, others below the bell curve. The statement, which can be connected with it, refers to the probability with which an event lies above or below.