Apples and oranges. No comparison. Genuine (as opposed to non-genuine, or hacked) refers to the validity of the code and key used to activate the installation. Retail (as opposed to OEM or VLK) refers to the packaging used to sell the software. Retail keys cannot be used with OEM or VLK versions and vice versa.
retail is store bought that can be used on any system that meets system requirements & oem is used only by dell, hp, toshiba, sony & other name brand computers not clone computers you put together yourself.
They are both the same thing. The retail you buy at the store. Once you install it in the computer it has to be registered/activated by microsoft over the internet/phone. Once Microsoft approves it, it becomes "genuine", that's there seal of approval that the product has been properly licensed to a particular computer/person. If it's not genuine, you won't be allowed to to download updates, and after a while microsoft will send a code that will let windows only work for 1 hour per day.
so you don't bother with updates.. and save a heap of money and time fixing everything they break.. by running borg or similar and being sensible. M$ don't make anything worth paying for..