Anyone who travels in Orthodox communites will have heard the phrase, "but it says in the Shulchan Aruch" spoken as an appeal to ultimate authority.
The Shulchan Aruch is accepted today as the authoritative code of Jewish law. It was compiled by Rabbi Yosef Caro (1488-1575), the great kabbalist and scholar who lived in Safed. Shulchan Aruch means "set table", as in all ready to eat. The name reflects Rabbi Caro's intention that the book would lay out the whole corpus of currently relevant halachah in an easily digestible form.
The main previous codification of the halachah had been Maimonides's monumental Mishneh Torah. Between Maimonides and Caro, the advent of printing led to a flurry of halachic books.
It seems that part of Rabbi Caro's intent was to critically evaluate these works. He expressed great awe of Maimonides and apparently did not intend the Shulchan Aruch to supersede the Mishneh Torah.
The Shulchan Aruch is divided into four sections. There's a famous story told in the name of a number of rabbis that the sage initiates a student into a fifth section of the Shulchan Aruch, "Common sense!"