There is a section for "broadcloth" in my local hobby lobby - it is nothing like what ckcowl is describing - all poly-cotton blends, pretty thin. More like what others have said, what button down shirts are often made of.
Before I knew better I used some in a quilt. It was a light color, and you can really see the seams where they overlap. Also my machine doesn't like working with it much, for some reason.
I've heard that there is such a thing as all cotton broadcloth, and I'd like to get ahold of some for shirts for my husband, but they sure don't carry it anywhere local to me.