Focus on the definition of a hydrograph: it's all about the discharge (flow) of water over time. Keep this in mind to avoid confusing it with other hydrological charts.
A hydrograph is a graphical representation of the discharge (or flow) of water over time at a specific location in a river or stream. It typically displays the relationship between the discharge and time, showing how water levels change over a given period. While rainfall and cumulative rainfall are related to runoff, a hydrograph specifically plots discharge, not rainfall.