There are many definitions for social justice. This one if from a United Nations website:  

 

The term 'social justice' implies fairness and mutual obligation in society: that we are responsible for one another, and that we should ensure that all have equal chances to succeed in life. 

 

The quote was taken from this page on Feb 12, 2015: http://www.unric.org/en/latest-un-buzz/29055-social-justice-for-all

A screen shot of the page is below: