سنة
Sunna
The Prophet’s example: his way of acting, which Muslims follow beside the Quran.
What it means
The Quran says that in the Messenger of God there is a good example (33:21), and commands obedience to him (4:59, 59:7). Much of how Muslims practise comes from this: the Quran commands prayer and charity, and the sunnah shows how the prayer is performed and what share is due as zakat.
The sunnah is known mostly through hadith, but the two are not the same: the sunnah is the practice, and the hadith are the reports of it.
Often misunderstood as
That Muslims follow hadith in place of the Quran.
What the sources say
The Quran is the first source, and the sunnah follows it; no sound report can overrule a clear statement of the Quran. The Quran itself directs readers to the Prophet to explain it, and a body of practice kept by the whole community, such as the number of daily prayers, is older and more widely attested than any individual report.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 35, listed as SUNNAH. The definition is restated here.