A normal probability plot is a graphical method for showing a frequency distribution. The scaling is set up so that if the distribution is normal, a straight line will result.
The normal probability plot is a graphical technique for normality testing: assessing whether or not a data set is approximately normally distributed. The data are plotted against a theoretical normal distribution in such a way that the points should form an approximate straight line. Departures from this straight line indicate departures from normality.