The Bell curve distribution is a common name given to a normal distribution. This states that for many variable occurrences, results tend to be centred on the average, at either extremes of the average the distribution sharply falls.
This graph of a bell curve distribution explains.
Graph of Bell Curve
A good example of a Bell Curve distribution is found in the distribution of IQ levels. Most people tend to be of average intelligence. Very few are either geniuses or dumb.