The concept of audience interactivity has been rediscovered across many domains of storytelling and entertainment—e.g. digital games, in-person role-playing, film, theater performance, music, and theme parks—that enrich the form with new idioms, language, and practices. In this paper, we introduce a Spectrum of Audience Interactivity that establishes a common vocabulary for the design space across entertainment domains. Our spectrum expands on an early vocabulary conceptualized through co-design sessions for interactive musical performances. We conduct a cross-disciplinary literature review to evaluate and iterate upon this vocabulary, using our findings to develop our validated spectrum.