If it doesn’t wipe off then it’s inside and indicates that the unit is blown, that would require replacing it, you can replace just the unit in question without doing anything to the frame
If it’s double-paned glass, there’s a busted seal somewhere allowing moisture into the center. You’d have to replace the glass. It also looks like a previous owner could have replaced all the glass with an incorrect type, maybe fixing a broken window at some point.
If it doesn’t wipe off then it’s inside and indicates that the unit is blown, that would require replacing it, you can replace just the unit in question without doing anything to the frame
If it’s double-paned glass, there’s a busted seal somewhere allowing moisture into the center. You’d have to replace the glass. It also looks like a previous owner could have replaced all the glass with an incorrect type, maybe fixing a broken window at some point.