Sunna, pl. sunan: “Road” or “practice (s).” Standard practice, primarily of the Prophet sallAllahu `alayhi wa-Alihi wa-Sallam, including his sayings, deeds, tacit approvals or disapprovals. Hadith Scholars add his personal traits – including physical features – to this definition.
The “sciences of the Sunna” (`ulum al-Sunna) refer to the biography of the Prophet (saws) (sira), the chronicle of his battles (maghazi), his everyday sayings and acts or “ways” (sunan) including his personal and moral qualities (shama’il), and the host of the ancillary hadith sciences such as the circumstances of occurrence (asbab al-wurud), knowledge of the abrogating and abrogated hadith, difficult words (gharib al-hadith), narrator criticism (al-jarh wal-ta`dil), narrator-biographies (al-rijal), etc. This meaning is used in contradistinction to the Qur’an in expressions such as “Qur’an and Sunna” and applies in the usage of hadith Scholars.http://qa.sunnipath.com/issue_view.asp?HD=1&ID=146&CATE=24
Probativeness of the Sunnah