Ixihtec

An ixihtec was a notion in Mexica culture of an intangible essence prescribing things properties. (PROSE: Against Nature)

Behind the scenes
Lawrence Burton noted that he coined the term in order to refer to the concept of a platonic form. However, the term is not quite used that way in the book, with Acamapichtli's ixihtec being transplanted into various characters. (One explicitly, one ambiguously.) In general, the term is used in similar ways to biodata, but there's no need for it to refer to a conscious mind, mirroring the cultural practices of the Mexica.