What is it? can you use it for quilt backing? fabric.com is having a good sale on it and wondered if I should stock up?

Here's what I found as a definition: http://www.textileglossary.com/terms/broadcloth.html

I would use the 100% cotton, but not the blend, but that's just me and MHO.

Instead of using broadcloth, which is a lil tougher to get a needle through that the 100% cotton when doing the actual quilting, I'd purchase the wide, 90-110" backings that are 100% cotton muslin. These backings are located in most fabric shops. I love the wideness due to not having to have seams in the wrong side of a quilt. You can often find a coupon, 50% off that you can use to buy this wide muslin by the yard cut. Just my opinion though - many chose to make the backing with a fabric they've used IN the quilt front - but it is very expensive. The muslin is what the women used in the Olden days!

If you plan on hand quilting be careful that it isn't too closely woven. I have used many different fabrics and that is the biggest issue for me. If machine quilting yourself, you can use almost anything you want without problems.

it's distinctly heavier in feeling than quilting cotton, so if you decide to use it, expect to feel the difference. also, quilting cotton won't wear as well. it's almost like men's workwear, not quite as tough as twill, but tougher than quilters cotton. it's got a different weave than twill, though. it's like a workwear shirt.
that's about as close as i can come to describing it.

if you wanted to make a quilt using all broadcloth, there's no reason not to. i just wouldn't mix them because of the difference in weight. i'm not the QP.