1) It is a graph in non-dimensional form that relates the Darcy-weisbach friction factor ($F_D$), Reynolds number ($R_e$) and surface roughness for fully developed flow in a circular pipe.
2) It can be used to predict pressure drop or flow rate down such a pipe.
3) Formula for pressure drop ($\Delta P$)
$\Delta P=\rho ghf$.
4) Moody's diagram can be divided into two regims of flow, that is laminar and turbulent.
5) For laminar flow Regime ($R_e\lt\approx3000$). For flow regime, the relationship between the friction factor $F_D, R_e$ and relative roughness $\dfrac \varepsilon D$ is more complex.
6) It was plotted by Lewis Ferry Moody in the year 1944.