Final answer:
A radio stream involves serving music up blindly (users can't select specific tunes), but keeping the flow of music in a user-directed genre.
Step-by-step explanation:
The type of stream that involves serving music up blindly (users can't select specific tunes), but keeping the flow of music in a user-directed genre is called a Radio Stream.
In a radio stream, users can choose a genre they like but do not have control over the specific songs that are played. This type of stream is similar to listening to a traditional radio station, where the DJ selects the songs within the chosen genre.
For example, streaming services like Pandora and Spotify's radio feature offer radio streams where users can select a genre or artist and the service will play songs from that genre or similar artists.