.dj is the country code top-level domain (ccTLD) for Djibouti.
It has been marketed for music-related sites due to the common use of "DJ" to mean disc jockey. A project is also under development to use it for "Data Journals". However, this TLD has not proven especially popular to date. Other similar ccTLDs are .fm, .am, .tv, .cd, .mu and .me. Such unconventional usage of TLDs in domain names are known as domain hacks.