Literally "way," meaning a way of doing things.
In the early stages of Islamic law, the sunna was the practice or way of doing things in a local community; legal decisions were often based on the established local sunna.
In the ninth century, the Prophet Muhammad's Sunna (usually capitalized in English) replaced local sunna as a basis for law. The Sunna is the sum total of all that the Prophet did, said, or even refrained from doing or saying; it is preserved in the form of hadith.