A Full-Buckel is a Mei Tai baby carrier with buckles at the shoulder straps and the hip belt. The buckles are needed to adjust the belt to the user. There is a buckle between the shoulder blades to prevent the shoulder straps from slipping down and to absorb the pressure onto the shoulders.
Often, there is a neck rest or hood as sun protection. Some models have darts to optimize the bagging and the sitting comfort. Strap and height of the back part are mostly adjustable as well. The buckles can be fixed to the hip belt before sitting age and to the back panel from sitting age.
Pictures (Click on the picture to see the sling):