What is the difference between the prefrontal cortex and frontal lobe?

Prefrontal cortex is a part of frontal lobe.

Our cerebral hemisphere is divided into 4 lobes : frontal, parietal, temporal and occipital. Among these lobes the frontal lobe is the largest. Here is a picture:

Each lobe is further divided in functional areas. The frontal lobe like other lobes has several functional areas. Functional areas are the areas of brain associated with specific functions. One of the functional area of frontal lobe is prefrontal cortex or prefrontal area. This area is associated with concentration, emotion and other higher brain functions.

In this diagram functional areas of the frontal lobe is shown : here we can see prefrontal cortex as a part of frontal lobe.

Here is a diagram showing all the functional areas along with their functions :