Ok cool, thanks! (Why couldnt they make it that simple on wikipedia? haha)
Of course I immediately had to go over to Wikipedia to find out what it said. And you're right, it doesn't help much, because it's a really poor article. I always imagine that if I'm ever tied down by a broken limb or house arrest or something, I'll finally have time to re-write all those inadequate Wikipedia articles I've found!
You do have to be careful with off-the-shelf acrylic gesso, though, as some of it isn't much more than white acrylic paint. It should have quite a bit of powdered chalk in it, which is what makes paints adhere to it. I've tried Golden and Liquitex brands and find them both too rubbery. Anyone have a recommendation for a gesso that dries a bit stiffer? Ideally you should be able to sand it smooth, but I'm not sure that's possible with any of the acrylic types.