Shi'ah , which means literally partisan or follower, refers to those who consider the succession to the Prophet - may God's peace and benediction be upon him - to be the special right of the family of the Prophet and who in the field of the Islamic sciences and culture follow the school of the Household of the Prophet.
Useful infromation: Shi'ism began with a reference made for the first time to the partisans of Ali (shi'ah-i ' Ali) , the first leader of the Household of the Prophet, during the lifetime of the Prophet himself. The course of the first manifestation and the later growth of Islam during the twenty-three years of prophecy brought about many conditions which necessitated the appearance of a group such as the Shi'ites among the companions of the Prophet.
The Holy Prophet during the first days of his prophecy, when according to the text of the Quran he was commanded to invite his closer relatives to come to his religion, told them clearly that whoever would be the first to accept his invitation would become his successor and inheritor. Ali was the first to step forth and embrace Islam. The Prophet accepted Ali's submission to the faith and thus fulfilled his promise.
It is obvious that because of such distinctive services and recognition, because of Ali's special virtues which were acclaimed by all, and because of the great love the Prophet showed for him, some of the companions of the Prophet who knew Ali well, and who were champions of virtue and truth, came to love him. They assembled around Ali and followed him to such an extent that many others began to consider their love for him excessive and a few perhaps also became jealous of him. Besides all these elements, we see in many sayings of the Prophet reference to the "shi'ah of Ali" and the "shi'ah of the Household of the Prophet."