Mishpat is today the modern Hebrew word for law. A mishpatan is a lawyer. The Israeli civil courts are charmingly called batei mishpat lshalom, courts for making peace between people. Mishpat Ivri is the name for those areas of traditional Jewish law that can applied to the areas usually covered by secular legal systems. Mishpat Ivri has standing in Israeli courts today.
The word is very ancient. Parashat Mishpatim in the Torah, read two weeks ago (Exodus 21-4), lays down basic civil law, including rules of damages, torts and ethical obligations to help the needy. Mishpatim also includes agricultural laws and rules about festivals.
Later mishpatim came to mean laws governing interpersonal behaviour. Medieval Jewish thinkers, including Maimonides, listed mishpatim as one of the main categories of Jewish law. Classically, mishpat covered ethical laws that were commonsense, with obvious reasons behind them, such as dont steal. These were contrasted with chukkim, laws such as the red heifer whose explanations were non-obvious, if they could be discovered by human reason at all.
Mishpat, a justly ordered society, is one of the foundational values of Judaism. The prophets railed against the absence of mishpat in the days of kings who abused their power.
Maimonides concludes his Guide for the Perplexed with the words from Jeremiah 9:23, Let not the mighty man glory in his might... let him glory only in this, that he knows me, for I am God who does lovingkindness, judgment [mishpat] and righteousness in the earth. Mishpat is one of the three key values here through which we imitate God.