Reverse Bias:

Reverse biasing happens when the diode's anode is linked to the negative side of the source, and the cathode is linked to the positive side of the source in Figure.  Holes inside the p-type material are attracted toward the negative terminal and an electron in the n-type material is attracted to the positive terminal in Figure. This avoids the combination of electrons and holes near  the  p-n  junction, and thus causes a high resistance to current flow. This resistance avoids current flow by the circuit.

Figure: Reverse-Biased Diode