1) Shiah or Shia, noun.1. one of the two great Moslem sects, centered in Iran, which regards Ali, the son-in-law of Mohammed, as the true successor of Mohammed and rejects the first three caliphs and the Sunnite book of tradition handed down under their protection.
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2) Sunni, noun, pl. -ni or -nis.
1. an orthodox Moslem; a Sunnite.
2. the Sunnites as a group.
Ex. The Sunni... compose about 90 per cent of present-day Islam (Newsweek).
You should know all about Sunnites, if you are one yourself.
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3) Mätam, the term used (mostly in South Asia) for the act of self-flaggelation during the Shia Remembrance of Muharram .
Please see:-
http://en.wikipedia.org/wiki/M%C3%A4tam