A "vinyl cover" refers to the protective outer layer made of vinyl material that is used to wrap and enclose something like an album or a book. It acts as a shield to protect the item inside and is commonly used for vinyl records. Full definition
There are some manufacturers who claim that they are selling organic baby mattress but it comes with vinyl covering to make it waterproof. (babieslounge.com)
Our crib mattress had some sort of vinyl covering on it so I guess it was waterproof. (corporettemoms.com)