Sankey: http://gojs.net/latest/samples/sankey.html

I believe it's called "Sankey Diagram" as denoted in the dropdown menu on the upper top left.

Here is the original demo[1] from Mike Bostock, D3's author.

[1]: https://bost.ocks.org/mike/sankey/

Though they have been around much longer than D3 has... https://en.wikipedia.org/wiki/Sankey_diagram

I believe it's called a Sankey diagram:

http://bl.ocks.org/d3noob/5028304

Sankey Diagrams. Useful for complex funnels!

We always just called them flow diagrams. I didn't know they had a specific name.

Where is the data from? It's a great overview of CO2 emissions, etc.