What files are served from webserver?

Hi, I've noticed a little info here: https://i.imgur.com/3bI7K12.png
I haven't seen this directory in provided path, what is it supposedly used for? What files are served from there?

all files you put there. E.g. if you want to have a custom remote control you can put the html file there and then access it for example from your smartphone via your local ip address.

The HTML file can then triggee whatever BTT action you want (see the docs for how to do that)