Not surprisingly, it's a religious technical term. Mahdaviat derives from mahdi, Arabic for "rightly-guided one," a major figure in Islamic eschatology. He is, explains the Encyclopaedia of Islam, "the restorer of religion and justice who will rule before the end of the world." The concept originated in the earliest years of Islam and, over time, became particularly identified with the Shi‘ite branch. Whereas "it never became an essential part of Sunni religious doctrine," continues the encyclopedia, "Belief in the coming of the Mahdi of the Family of the Prophet became a central aspect of the faith in radical Shi‘ism," where it is also known as the return of the Twelfth Imam.
Mahdaviat means "belief in and efforts to prepare for the Mahdi."
In a fine piece of reporting, Scott Peterson of the Christian Science Monitor shows the centrality of mahdaviat in Mr. Ahmadinejad's outlook and explores its implications for his policies.
As mayor of Tehran, for example, Mr. Ahmadinejad appears to have in 2004 secretly instructed the city council to build a grand avenue to prepare for the Mahdi. A year later, as president, he allocated $17 million for a blue-tiled mosque closely associated with mahdaviat in Jamkaran, south of the capital. He has instigated the building of a direct Tehran-Jamkaran railroad line. He had a list of his proposed cabinet members dropped into a well adjacent to the Jamkaran mosque, it is said, to benefit from its purported divine connection...