This unique card fold is referred to as a Diamond Front Gatefold Card. I love that the oversized tag holds the card closed when inserted in the front diamond aperture!
The 4/29/14 blog entry of Dena’s Stamping Corner that can be found HERE, featured an awesome example of this card style that had me hooked the moment I saw it. Even better yet, her post linked to several tutorials that provided detailed steps and measurements, so that I was able to create one of these cool cards myself!
Closeups of the inside of the card: