The "banana braid" is a style of braid where strands of hair are braided along the length of the head, usually starting at the nape of the neck and moving up towards the crown of the head, creating a shape reminiscent of a banana .
"D-4" could be an internal code or manufacturer-specific designation for that style or size of banana braid. The ":1/8" could indicate a specific size, although this may vary depending on the designation system used.
Without more context, it is difficult to give a precise interpretation of this mention. If you need more detailed information about this product or designation, I suggest you consult the details provided by the manufacturer or seller for further clarification.