The term 'Wonderfilled Cookie' is a reference to the popular Oreo cookie. Oreo is a sandwich cookie made of two chocolate wafers with a sweet cream filling in between. It was first introduced in 1912 and has since become one of the most popular cookies in the world. The Wonderfilled Cookie is a special version of the Oreo that was released in 2014, featuring a new cream filling that is flavored with marshmallow, caramel, and other flavors.