What is meant exactly by the description 'more musical'?

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.

I’m going to add to what @mapman has pointed out. Musicality has everything to do with how the amp makes distortion. The main differences we hear between amps, their ’sonic signature’ is in fact their distortion.

To be musical, that distortion has to be benign to the human ear. The only harmonics that qualify in that way are the 2nd and 3rd.

Higher ordered harmonics, the 5th and above, are sensed by the ear and interpreted typically as harshness and brightness. In musical instruments, the higher orders are sculpted by the instrument maker as the tone colors of that instrument. IOW distortion is sensed by the ear in the same way that the ear hears tonality in musical instruments.

Fortunately, if the 2nd and 3rd harmonics are high enough in amplitude compared to succeeding harmonics, the latter can be masked. The result is even though the higher orders are present, the presentation can be smooth and detailed, which is to say ’musical’. Tube amplifiers are very good at this sort of thing, which has kept them going the last 70 years. Solid state has been challenged by this issue because while they typically make less of the higher orders, their higher orders are not masked.

The ear is keenly sensitive to the higher ordered harmonics because it uses them to sense how loud sounds are. The ear has over 120dB range and frankly, a lot of solid state amp designers didn’t take that bit into account, so unmasked higher ordered harmonics will cause the amp to be harsh and bright; i.e. not so musical.

This is a bit of a nutshell description of the issue.

You'll know it when you hear it. 

some amps are about the sound; meaning you are more aware of pieces of the sound....bass.....detail.....high frequencies.....maybe impact and aggressive beat. it might sound very clean and even scrubbed a little. note decay can be clipped. certain electronic music is complimented by this presentation. these amps strangle the music to a degree. clinical.

a few amps are about the event, the intensions and artistry of the performers, the vibe of the venue, and immersion into the rich tone and textures of the nuance and feeling of the musical energy. the beat might not be as impactful, but it carries you along more into the essence. these amps get out of the way of the music. musical.

there is more to these things than amplifiers, there is the context of the speakers, room and system....and the type of music and quality of the source.

but amps do play a big role. this is not a tube<->solid state thing. but it is related to simplicity of circuitry and keeping the processing to a minimum. zero negative feedback helps. efficient speakers help. a great first watt helps. the music can’t be held back.

some amps can be musical, but too colored to be effective with all types or scales of music. but that might your preference. personally i want an amp to sound like music, and not have any sameness of coloration i have to listen through.

+1 @mapman

I have resisted the term, because whatever someone prefers in the character of their system is going to be the one which draws them into the music, no?

If that’s true -- and I cannot see how that can be disputed -- then every system which someone likes is "musical."

What if someone’s ear does not care about the kind of distortion @atmasphere identifies with musicality? Would we say their use of the term "musical" is incorrect? This would be tantamount to saying that "good food is spicy food" and then for anyone who demurs, they like "not-good" food. Would we say that some people like "not-musical" amplifiers?

That said, I do see that some here are trying to help associate the word "musical" with its most frequently used associations -- lexicography, if you will. It's "rhythm and pace" or "2nd and 3rd order harmonics," etc. Maybe that's useful. I'd still expect a lot of people to just use the word to mean other things, and not really be incorrect in their usage. This makes the word of suspect usefulness.