...
Raw Stream: The audio stream, (typically "raw" PCM), as coming from a source. There shall be none or minimal application of Volume (stream should be at maximum volume), Effects (no effects applied), or mixing (one stream per source).
Raw stream metadata: Information about the stream, where it is coming from (an app? the HMI? the system?) and the type information (media? navigation prompt? urgent message?). Metadata is used in an external mixing and effects system to take the decision about how to mix, how to apply priority of one sound over another, and so on.