Box joinery (also known as box joint) primarily joins sides to create boxes, both large and small, such as trunks, chests and drawers. Notches are cut to fit in an interlocking manner, increasing surface area to permit for more glue strength and requiring minimal (if any) fasteners. Box also helps to keep the parts square. Originally an extremely functional kind of joinery, it is now often employed as a decorative furniture component.
The notches cut in box joints correspond to the depth of the adjoining planks.
R J Hoppe Inc
This desk perfectly illustrates the use of box joinery in drawers.
This pub showcases box joinery where the side meets the top. You can obviously see the interlocking planks in the corner.