Although some games that I have been in have added the "fullblood" category between pureblood and halfblood, I have gone with J.K. Rowling's designations on the individual characters' pages and here: pureblood = 4 wizarding grandparents; halfblood = at least 1 wizarding parent, at least 1 muggle grandparent; muggleborn = 2 muggle parents; squib = at least 1 wizarding parent.