That’s usually just water or some chemical that was sitting for a while. Try a Meguiar’s foam pad and some light polish in a circular motion. Don’t apply really any pressure at all. If you apply a lot of pressure you could cause hazing in the glass. You aren’t buffing the glass, you’re just trying to wipe it clean. Maybe try on a corner or area you aren’t worried about messing up. Also note, some polished and waxes could cause a temporary haze as the product will stay on the glass itself for a period of time. Similar products like Rain-X do this. Rain-X works, but it always leaves a haze.

I think the problem you’ll run into is it’ll keep coming back. Similar to how the water always goes the same patter around where your wipers are even if you aren’t using them. You always see that curve where the wiper wipes the windshield. You can temporarily fix it with the method above, but it’ll probably keep coming back. Whatever you do, don’t mess with the defroster lines in the back window! They’re more pain than it’s worth.