A Branded Short Domain (bsd) is a the domain that takes the place of “bit.ly” or “bitly.com” in a shortend URL. Adding a Branded Short Domain to your bitly account is free of charge although you must purchase a bsd from a third party domain registrar. Domai.nr, GoDaddy, and 101domain are great places to begin your search. You can buy a BSD here. Keep in mind that your bsd must be 15 characters or less, including the dot.