Social Justice spends a lot of time getting bounced around. Often it is used as an argument to support this or that new fundamental human right, often related to healthcare.
The idea seems to be that if you cannot earn enough to afford something, and politicians think you cannot have a good life without it, you should have it anyway.
The UN defined it as "fair and compassionate distribution of the fruits of economic growth."1 Though I note they don't define fair to who, the contributor to the pool of funds being distributed or the recipient.
The UN went on to say, "Social Justice is not possible without strong and coherent redistribution policies conceived and implemented by public agencies."
Well, now we know who is going to use force to cause contributors to put into the pool.
This goes beyond the idea of a social safety net, which garners wide support, and onto the idea of "fair" distribution.
Accurate Reality: Social Justice may have a significant philosophical basis. The way it is used today is primarily a high sounding term meant to support politicians deciding what and how much people "deserve" instead of voluntary free exchange deciding and then using the coercion of the tax authority to take it from some and deliver it to others. This is beyond providing a safety net for the poor, old and disabled.
1) "Social Justice in an Open World: The Role of the United Nations", The International Forum for Social Development, DEPARTMENT OF ECONOMIC AND SOCIAL AFFAIRS, Division for Social Policy and Development, ST/ESA/305". New York: United Nations. 2006. p. 16.