When I look at the way people talk about justice, I see that they tend to fall into two broad camps:

1. Justice as a Set of Ideals:                       

Norms of justice tells us how a society would have to be structured to be morally flawless. Satisfying these norms does not make a society literally the best imaginable from a moral point of view, but it does put it and everyone within that society above moral reproach.

E.g., G. A. Cohen

2. Justice as a Problem-Solver:

Human beings face a problem: how to live together in morally good way despite having conflicts of interest, limited altruism, and limited competence. “Justice” refers to the moral norms that would make the best of this situation, without imagining these problems to have gone away.  A society that eliminates even potential conflicts of interest, has perfect altruism, etc., doesn’t achieve justice, but transcends it.

E.g., David Hume, David Schmidtz

I honestly don’t know if questions about justice are about 1 or 2. In common language and in the philosophical tradition, there are grounds for going either way. I’m also not sure whether anything of philosophical importance that turns on making a choice about whether "justice" refers to 1 or 2.  I do think that that both sets of issues are worth exploring from a philosophical point of view, though from a practical point of view, 2 is more important than 1.