what is meant by neural networks interval plot

hi there,

im building a MLP network .....however,while training netwrok nntraining tool gui automatically opens, at the end of this gui there is a scale placed at the bottom showing plot interval against epochs, i dont know why its placed there and what its used for , i noticed as i increase the value of this plot interval by moving slider , training rate increases & training time decreases......does anyone know what is meant by this interavl plot???