Sunnah denotes a practice established from the Prophet ﷺ within the prescribed way of worship. Jurists sometimes distinguish a sunnah from a merely recommended act according to emphasis and regular observance.
Leaving a fard invalidates the required act of wudu, while leaving a sunnah does not necessarily invalidate wudu. Yet habitual abandonment of an emphasized sunnah without excuse is not treated as trivial. This distinction helps explain basmalah, siwak and repeated washing.