Bell Curve
This is statistically a large and random sample which, when measured, will produce a bell curve on a bar chart - the scale measurement being along the x-axis and the total occurrences within the sample up the y-axis.
If one took as a sample all the inhabitants of Greater London as a suitably large group and then made measurements i.e. height, weight, or wealth, a distribution would occur around the mean. Hence, there would be few at the extremes - the majority being near to the middle. This is defined on a Market Profile chart as the Value Area .