Islamic law, as revealed in the Qur'an. Many areas are covered, including behavior, government, diet (see also halal), the practice of worship, and whatnot. When strictly applied, Shari'ah seems harsh to most Westerners; we've all heard about the Taliban in Afghanistan cutting hands off thieves and requiring women to wear the chador (which isn't just a veil).
Heed Jaez; I'm leaving this here only so his reference to it will make sense.