What does it mean when a vinyl record says "Limited to 700"?
It's a limited release, they only pressed 700 copies. It's intended to make the copies more valuable (similar to limited releases of prints for visual artists).
According to this site, it looks like there were other releases of the album, but only 700 of the gray-and-black swirl limited edition vinyl.
This site specializes in limited releases, you can compare some of the others they have listed there.