Which of the following count as "whole" grains for diet puposes?
Brown rice - I know this one
I'm not sure what you mean by "diet purposes" but a whole grain is - ummmm - a whole grain. Other than brown rice, all the others you mention have been processed from the whole grain in some way, by cracking/using only part of the grain/precooking/milling.
An easy way to find definitions of these (and any other) terms is to go to Google and type in define: <your term here>
doesn't appear this way. A straight google search for burghul
indicates it is simply cracked wheat. Bulgur
, on the other hand, is is wheat that has been steamed whole, dried, then cracked.
And, as you probably know, polenta is a dish made from cornmeal. In the USA we called it corn meal mush, that that didn't sound so great on restaurant menus.