BookBaby has many distribution partners and they each have their own restrictions to metadata. We send the same information to all of our partners, so in order to take advantage of their different descriptions, we offer our clients two different description fields – a short and long.
The difference is in length only, so if you have a long description that fits in the short description field, you can feel free to use that for both. Amazon uses the long description, while Apple uses the short description. Other sites vary.