Sankey diagrams are a powerful visual tool for understanding how data flows through a system. They provide a visual representation of the connections between different elements of a system, showing how data moves from one point to another. Sankey diagrams can be used to
From Wikipedia
Sankey diagrams are a data visualisation technique or flow diagram that emphasizes flow/movement/change from one state to another or one time to another, in which the width of the arrows is proportional to the flow rate of the depicted extensive property. The arrows being connected are called nodes and the connections are called links.