The impurity (najāsa) that must be removed from the body with water is divided into two types: Conventional (‘Urfī) and Legal (Shar‘ī).
Conventional: Such as excrement, urine, and all other dirts of the body.
Legal: Such as Janāba (ritual impurity following sexual discharge), which necessitates water and its pouring over the entire body and the parts which water can reach; and the "events" (aḥdāth) that necessitate Wudu (ablution), which is the washing of specific limbs and designated organs for every Muslim upon the intent of entering into prayer, according to His—the Mighty and Sublime—saying: {O you who have believed, when you rise to prayer, wash your faces and your hands to the elbows and wipe over your heads and your feet to the ankles} 1 .
The outward meaning of the command is understood.
The Inner Meaning of Wudu (Bāṭin al-Wuḍū’)