Ever seen a video with graininess, like perhaps the Blu-Ray Stargate scenes that were filmed inside structures? It is like that but with sound. Not something added, like with distortion, or something skewed/smeared like with muffling, but detail missing. At least that is my interpretation....
In the case above, you likely wouldn't even notice the missing detail unless comparing it to something more transparent sounding. Other things could contribute to the lack of detail as well, making my observations imperfect since I never put a pair in my listening room space for a more spot on observation (such as extreme amounts of wall reflection interference). That is why I state it as IME and IMO.
I agree about the confusion concerning terminology. I am confused about a lot of it also, so I apologize if I used any terminology incorrectly.