In Islam, ablution or ritual purity, rahara, is required before conducting religious duties, especially the salat. There are two types of ablution: ghusl and wudu, regulations for both are given in the Qur’an. A third type, tayammum, may be substituted for wudu, and occasionally for ghusl. This method is used in necessity when water is not available; clean sand is used instead and rubbed upon the body to purify it. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, pp. 8-9