Quantile-Quantile Plot
A quantile-quantile plot compares ordered sample values $x_{(k)}$ with theoretical quantiles from a reference distribution $F_0$. It is a graphical diagnostic for checking whether data plausibly follow a target family of distributions.
In the simple case, plot $x_{(k)}$ against $F_0^{-1}(t_k)$ for $k = 1, \dots, n$, where $t_k$ is a plotting position such as
$$t_k = \frac{k-0.5}{n}.$$If the model is appropriate, the points should lie approximately on a straight line.