Refers to Dolby Digital Plus audio with 6-channel surround sound (5 main speakers and 1 subwoofer).
The (Web Download) designation is critical for assessing quality. This means the source material was directly downloaded from a streaming service (such as Apple TV, Amazon Prime, or Maxdome) without being re-encoded.
Given this information, here's a guide on what you might expect and how you might handle or enjoy your video: