what is formx referring to? (ajax)

I recieved an answer on how to get some particular ajax to work and part of the solution was these lines:

ndxcar1 = document.forms.formx.one.selectedIndex;
car1 = document.forms.formx.one.options[ndxcar1].value;

what the heck does "formx" refer to?

Here is the code in context:
https://www.experts-exchange.com/questions/27664886/Can't-get-AJAX-to-work-very-simple.html?anchorAnswerId=37815202#a37815202