Sankey diagram depicts flows of any kind and their quantities in proportion to one another. It was named after Matthew Sankey, an Irish Captain, who, in 1898, drew a chart showing the energy efficiency of a steam engine which was pretty much the same as the present one.
This chart represents nodes connected by lines or arrows. The width of the lines depends on the amount of flow from source to target: the bigger the quantity, the wider the line.
Sankey diagrams are popular in science, especially physics area. They often used to show the transfer of energy (inputs and useful and wasted output) and some other resources but are also acceptable when describing different processes and their states.