Clojure/EDN feature where a keyword carries a namespace prefix (e.g. :youtube.video/id vs :youtube.channel/id). In the talk, namespaced keywords are the cornerstone of context-free API design: seeing :youtube.channel/title anywhere in the codebase makes its meaning unambiguous without surrounding context, and fully-qualified names let different services (YouTube, SpaceX) share the same identifier concept by aliasing.