I like Elena Pilipets (et.al.)'s term synthetic imaginaries so tried to figure out more of the background for the use of the term synthetic media. As far as I can tell the first use in the sense of AI-generated content was 2018. Synthetic is often interpreted as "artificial" and even as "fake" but Elena insists it's about synthesis, creating something from many parts, and also the human and AI participating in this. https://jilltxt.net/synthetic-imaginaries-and-synthetic-media/
Professor of Digital Culture and Co-Director of the Center for Digital Narrative at the University of Bergen.