the.com/bell curve

means A symmetrical, bell-shaped graph showing that in most natural and human measurements, the majority of values cluster around the average, with fewer and fewer cases as you move toward the extremes.

from Formally called the 'normal distribution,' it was worked out by mathematicians including Abraham de Moivre in the 1700s and later Carl Friedrich Gauss, which is why you'll also hear it called a 'Gaussian curve.' The 'bell' name is simply descriptive folk shorthand that stuck once people started plotting the data and saw the curve's unmistakable bell-like shape — a high rounded peak in the middle tapering symmetrically into two long, thin tails.