Where does the 'J' in SSJ and SSJ2 come from? In Dragon Ball Z, the abbreviations for Super Saiyan 1 and 2 are SSJ and SSJ2. However, there is no 'j' in Saiyan, so where does this 'j' come from in the abbreviation?
It comes from the Japanese original name for Super Saiyan: 超{スーパー}サイヤ人{じん}, pronounced Sūpā Saiya-jin.

You can read more about it at http://dragonball.wikia.com/wiki/Super_Saiyan.

Jin means "people/person." 'Gaikoku-jin' means foreigners.