How is this function called??

When you scroll down the a page a vertical 'progress bar' fills up showing where you are / where the project is. See image

Hi, my name is Erik. I'm building a landingpage with a roadmap in it and this would be a cool visual way to communicate.

I'm looking for information on how you call this so I can search for it.
Also if you know how this is made all info would be a great startingpoint for me.

Kind reagrds