The term musical refers primarily to rhythm and pace. As one learns what different terms mean starting as a novice… the real obvious stuff is treble, bass… imaging, microdetails, grain,… etc… one generally learns down a path of more subtle characteristics.
Rhythm and pace is like noice floor. It is profound but not something easy to put your minds eye on. It is the core musical connection… the emotional connection. It is what makes you want to tap your foot or in extreme circumstances get up and dance. The emotional connection to the beat… well rhythm. It seldom happens without midrange bloom… but it can… midrange bloom is the fully nuanced and laid out to hear midrange really helps to close your eyes and get sucked into the music.
It took me decades to actually be able to put my finger on it instantly. I can now, with no problem and gauge how good. Long ago there was a tendency for equipment that had great Rhythm and Pace to lack detail (tubed stuff is much more likely to have great rhythm and pace). This is not true now. Over the last decade Pass amps have gotten much better for instance.
The opposite is dry and analytical. You sit and appreciate all the details and slam, the imaging, but after 45 minutes you get bored. Your body has no desire to move with the music.
I recently auditioned three integrated amps, a Luxman, Pass, and Audio Research ($10K each except the the ARC $6K). The Luxman was high on details… very trebly offset by punchy bass… great transparency… completely devoid of rhythm and pace. The Pass, real sounding treble, nice round bass and a core that made me tap my foot and move in the chair. Audio Research, my eyes instantly closed and I was completely engulfed in the music (not the details and sound… the music… the desire to more and be emotionally pulled by it. That is great rhythm and pace.