Incanters are a subset of the avout linked to the Halikaarnian orders who, according to Saecular legend, are able to alter reality through the incantation of certain coded words or phrases. This physical change is somehow accomplished through Polycosmic Manipulation.
Fraa Jad is an incanter, and is described by Fraa Erasmas as a "mad sorcerer." Several times in the book, Jad explores millions of possible futures at random (by placing tiles, pressing buttons, etc) then forces his Narrative to the single one he prefers. This technique is akin to the functioning of a quantum computer, which (in theory) tests all possible solutions to an equation simultaneously, then collapses its wave function to the correct answer.
There is some similarity between Fraa Jad and Enoch Root from the novel Cryptonomicon and the The Baroque Cycle. Furthermore, the concept of changing reality through the incantation of certain words is a familiar Stephenson idea, dating back at least to the use of Nam-Shub in Snow Crash. The nature of Fraa Jad's chants are suspected to be Buddhist.
There is some similarity between Stephenson's Incanters and Stanislaw Lem's School of Higher Neantical Nillity.