It's called scrapbooking paper. You make cards, scrapbooks and much more with it. It is too thin to be cardstock. So it is probably just regular scrapbooking paper
The paper is not 6x looks more like 8 1/2 x 11 regular size paper. 6x4 would be more square not rectangle. As I use scrapbooking paper all the time for making scrapbooks and cards. Hope this helps since this person is unsure and had never used it. Glad to everyone.