1. Jigga is a shortened form of the old racial epithet 'jiggaboo' commonly applied to African-Americans well into the 1970's.
2. Jigga is one of the many nicknames for Jay-Z, put Nigga and Jay-Z together and you get Jigga. "Y'all can never diss Jigga, get nothin for that" -- Jay-Z featuring Kid Capri (It's Like That) [1]
3. A less inflammatory alternate for the word nigga.
http://tinyurl.com/yhqzxo7 Nice to know that our President is 'down wit' this kind of stuff...
I would be embarrassed to know all that.