Excerpted from Wikipedia:

Political philosophy is the study of such topics as liberty, justice, property, rights, law, and the enforcement of a legal code by authority: what they are, why (or even if) they are needed, what, if anything, makes a government legitimate, what rights and freedoms it should protect and why, what form it should take and why, what the law is, and what duties citizens owe to a legitimate government, if any, and when it may be legitimately overthrown—if ever. In a vernacular sense, the term "political philosophy" often refers to a general view, or specific ethic, political belief or attitude, about politics that does not necessarily belong to the technical discipline of philosophy.

For more information see Wikipedia: Political Philosophy