The primary goal of Political Philosophy is to provide a systematic account of the concept justice.
Broadly speaking, justice is defined as that which is due to someone in a social context. Or, it can be defined as that to which an individual has a reasonable expectation. What, exactly, one owes to another, or what, exactly, one has a reasonable expectation to, will vary depending on the political theory.
There are two distinct applications of justice in the organization of society: Commutative Justice, and Distributive Justice.