A hearty welcome to you, carpedm. I'm pleased that you have seized the day to pose this question. For lack of a better term, I'd call them inserts. An irritant certainly. There are the free-floating kind that land in your lap or on the floor, as well as those stapled at the center, requiring you to rip them out from two different parts of the magazine, trying not to tear the pages. I always get rid of the critters as soon as a magazine arrives, a process I call deboning.