Well, a glycosaminoglycan is a special type of polysaccharide that consists of repeating disaccharide units. So we have two sugars that repeat again and again and again. Now, one of these sugars is an amino sugar. And what that means is it contains an amino group. And at least one of these sugars in the repeating disaccharide unit is actually modified with some type of negatively charged group. For instance, a sulfate group or a carboxylate group.