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

I did not wrote history... 😊

Before the Edison and Charles Cros gramophon invention at the same year, euphony and harmonious was refering to the sound of music well played or sang in well realized acoustic architecture location ...

This adjectives then refer , to acoustics parameters in some location with very well trained musicians...

The word "musical" as an adjective to qualify a sound perception as harmonious and euphonic refer as well to acoustic as music itself together and this adjective predate Edison invention and then is older than any gear system ...

Then when we qualify the sound impression of any pieces of gear for specific trained ears in some acoustic room "musical" it refer to an acoustic impression and a musical impression together when the gear piece under test listening do not impede the awaiting results pertaining to what is an harmonious and euphonic perception in some specific acoustic conditions for the AVERAGE human ears ...

Many speakers are tested by the designer in anechoic room to verify their potential musicality by testing their frequencies response but it can be done in normal room with the necessary equipment ...Anyway acoustics parameters of the room must be known.... Any designer know that speakers /room will give an impression different if we change the room materials acoustic content, geometry, topology and dimensions etc ...

Then acoustics parameters knowledge are important for the definition of a "musically" subjective well accepted experience for most human subjects...

The gear choice matter for sure ... I just bought a tube preamplifier for my active speakers and the improvement is amazing... But no gear change can repair or compensate acoustics, in reverse no acoustic change will compensate or redeem a bad gear choice...

When our gear synergy and choices are done , no upgrade of a single piece of gear will compare to room acoustic parameters well done ... The only exception will be going from a very bad cheap piece of gear to a top very high cost one as for speakers choice ... No room acoustics can redeem a bad speaker or very low cost one compared to a TOP one... In reverse TOP speakers in a living room, even a good room , will not sound as the same speakers in a carefully dedicated room ... There is a difference between any speakers at any price giving his minimal working sound quality and the same speakers giving his maximal sound quality... The difference will be room dependant generally more than from change of comparable amplifiers choices or dac choices near the same price bracket ...

Acoustics is the more underestimated factor ... But even cables matter, i just change one of mine from cheap to better .. 😊

the most important factors when the gear choice and minimal synergy is reached are the electrical noise floor embeddings controls, the mechanical vibration/resionance controls and the essential acoustic parameters controls...Without these three controls under your hand , any upgrade will be premature and perhaps useless...

The Merriam define "musical" as harmonious and euphonic experience as HISTORY taught it because thousand of years of successive musicians and acoustician define the territory with experiment and knowledge of what is "musical" experience in music history as in acoustics architecture and applications

You obviously took different history courses than I did.

I guess opinion and taste might enter into it?

No accounting for taste.

As far as what makes equipment sound musical, that is very predictable, For those who do not understand engineering, their opinion will matter (to them), but that won't change how equipment behaves...

No accounting for taste.

As far as what makes equipment sound musical, that is very predictable, For those who do not understand engineering, their opinion will matter (to them), but that won't change how equipment behaves...

Sure,  @atmasphere  , but what is meant by "more musical"?

@mahgister  you continually use words like "impression" and "perception" and "well."  "Impressions" describe subjective experiences, "perceptions" describe subjective experiences, and what some consider "well" others do not, so "well" is also subjective.

OP asked "what is meant by more musical"?

Musical = pertaining to music, as in a musical instrument such as the cornet.

Unless the term music is also subjective, that definition is not subjective.

When a reviewer writes that "a certain piece of gear is more musical,"

I would assume that the reviewer means that the gear produces music "well" and that the experience is listening to something  "having the pleasing harmonious qualities of music."  However, what pleases some does not please others and what some find harmonious others do not.

I have nothing at all against Cher Bono or her heritage--however I find nothing harmonious or pleasing about her nasal catterwalling in a monotone about being a half breed.  I would say the same about the thrash-metal sound of the band Mega-Death.  My perception or impression of both is that neither meets the criteria of being very "musical."

But there are a lot of people who would argue that I am wrong about both (however, it wouldn't be the same group of people that would argue that the sound of Cher is musical that would also argue that thrash-metal is musical).

When a reviewer writes that "a certain piece of gear is more musical,"

"More musical" means an upgrade of gear or /and upgrade of room acoustics...

If you own atmasphere top amplifier for example which is designed in account of some psychoacoustics facts, then you may try to upgrade instead of his already TOP amplifier a low cost speakers to a better one , but if your speakers are relatively good already BEFORE upgrading, it is better to improve the room ...

One piece of Gear upgrade at some level of price toward another gear piece in a similar price scale will not compare generally to the huge impact of room dedicated acoustics at all ...

What you seem to MISS IS that anything , any piece of gear will sound in synergy with all the other piece of gear but IN A DIFFERENT WAY in a different room ...The room acoustic will make a HUGE difference on speakers impressions...

If the room is bad, or if it is not bad but a simple living room or if it is a dedicated tailor made room acoustically controlled for a specific pair of speakers then you have here 3 cases of two increase in .SQ .. A bad room versus a good room with no acoustic control or/and treatment , and now going from a good room without any acoustic optimization to a dedicated acoustically controlled room ... Most gear upgrade will not compare to that if you already own a synergetical system already then upgrading anything is way less impactful than upgrading the room ...

Now dont believe any  reviewer when they say that a piece of gear is " more musical "... It is relative not only to the design of the piece of gear but also to the synbergy with the other gear pieces  but also to the room acoustics ... There is too much factors at play here to believe one reviewer...

I believe atmasphere because he knows psychoacoustic facts  about human hearing which he use in his design to improve it and make it more musical...Then the only way to make the amplifier of atamasphere "more musical" if your sperakers are on the same level is giving to the system a dedicated acoustic room the best as possible in your house ...