hey there thriftymae, i might be wrong, but i think parboiling is basically just like, partially cooking something before you really cook it. you know, kinda like a prep step.
i've done it a few times for potatoes before grilling them for a cookout, and it really seems to help them cook through more evenly on teh grill without burning the outside first. i've also heard of people doing it for things like sausages or ribs before putting them on the smoker, though i haven't tried that myself yet. it's supposed to make them more tender from teh start. it feels like a bit of a cheat sometimes, but it does make things easier, especially when you're trying to get a lot of stuff ready for a big bbq. maybe try it for some veggies next time you're firing up the grill? it can really make a difference, especially for denser vegetables that take a while to cook through. i hope that helps a little!