normalpdf( is the normal (Gaussian) probability density function.
Since the normal distribution is continuous, the value of normalpdf( doesn't represent an actual probability - in fact, one of the only uses for this command is to draw a graph of the normal curve. You could also use it for various calculus purposes, such as finding inflection points.
The command can be used in two ways: normalpdf(x) will evaluate the standard normal p.d.f. (with mean at 0 and a standard deviation of 1) at x, and normalpdf(x,μ,σ) will work for an arbitrary normal curve, with mean μ and standard deviation σ.
For the standard normal distribution, normalpdf(x) is defined as(1)
For other normal distributions, normalpdf( is defined in terms of the standard distribution:(2)