I say, and with God's success: it is the wiping of the place of excretion or washing it. The excretion (najw) is what comes out from the abdomen. It is permissible that the ‘s’ is for request: like ‘extracted’, meaning requesting the excretion to remove it. It is a Sunnah with water or stone or similar if the excretion does not exceed the size of a dirham; as narrated by Abu Huraira (may Allah be pleased with him), he said (peace be upon him): "Whoever uses stones for cleaning, let him do it in odd numbers; whoever does that has done well, and whoever does not, there is no harm on him," in Sunan Ibn Majah 1: 121, and Sunan Al-Darimi 1: 177, and Musnad Ahmad 2: 371, and Sharh Ma'ani Al-Athar 1: 121, and Allah knows best.