Do you know ghouls from goblins and ghosts?
(Or "Gaussian distribution") The frequency distribution of many natural phenomena such as the height or intelligence of people of a certain age and sex. The formula looks something like:
P(x) = e^(((x-m)/s)^2)
where P(x) is the probability of a measurement x, m is the mean value of x and s is the standard deviation.
Also known as a "bell curve" because of its shape.