I'm not sure but I suspect it is an update to the updater which I got some months ago. If it is already installed it won't appear. Why don't you click on it and see. (Make a restore point first)just in case.
I've just installed it and run it and it seems to be designed to update all of MS products though windowsupdate - at least it also gave me an update for MSOffice 2003 which I've not had through windowsupdate in the past.