From IFWiki

A term (short for "interactive") used by Neal Stephenson to describe a form of elite interactive entertainment, in which a live human performer (a "'ractor") working from a computer-provided script, improvises in real-time with paying customers, over a virtual reality network. This imaginary genre, a cross between improvisational theatre, interactive fiction, and mass-entertainment such as TV, features prominently in Stephenson's novel The Diamond Age, or, A Young Lady's Illustrated Primer.