What define "musicality" ? And what constitute "musicality" in audio ?

I am going to have to agree with this, with the caveat that a quality system can intensify the feeling.

Oregonpapa
Musicality has to do with pace, the expert playing of the musicians, the correct tonality of the instruments, the layering of the instruments, and/or the proper positioning of the players on the sound stage. When it all comes together, that is musicality.

I don’t think musicality has much to do with audiophile terms, like transparency, and such. I’ve heard musicality on the car radio, even to such a degree that I’ve stopped the car, written down the name of the artist, then driven over to the nearest record store to buy the music.

and this, without the emphasis on the system

millercarbon
Musicality I think is one of those terms people use for when the system or component sounds good in a way that you are trying to think of exactly how it sounds good but its hard because your foot starts tapping and your heart starts racing and your mind keeps returning to how goddamn good it sounds so quit bugging me man just go away and oh yeah damn that sounds good!

Musicality has peaked when that chill runs down the back of you spine.

But plenty of people use the term "musical" to describe how a system sounds, not just how a performance sounds. That makes it sound like two different things.

I think that no musical hall or concert hall sound the same, and no individual room either; and the performance is linked to the location of the interpreters and the location of the listeners, sometimes 2 different locations that the audio grid linked together... Not only there is engineering factors in the experience of listening music, architecture of the concert hall in the lived experience, audio engineering also, audio electronics in delayed experience, there is also the individuality of the hearing body of each of us with our own past experience... The experience of "musicality" is linked to all that I think...But one thing is fundamental, each of us, creator of music or listeners, we all crave for "musicality" in the concert hall or in our audio room...I want to know the factors that contribute to this experience in our audio experiments in our own room... That reduce the experience to the audio side of the story and the personal factors in our own history with the experience of the reproduction of music... I will leave the creative side of the story to philosophy of music and of musical performance... I want to read each of us about his personal experience with his audio system in his room..... 

What are the most  important factors, or perhaps the single more important one, that contribute to your own experience of "musicality" ?I will learn something...

It's a lazy meaningless term. The proof is in the fact that someone decides to defend it in the OP. It is like calling food "tasty". Good audio writers never use the term because they don't have to. They have the writing skills to describe what they are hearing without resorting to meaningless shorthand. It also gets thrown around more often with regard to low to mid-priced gear. It bothers me less than PRAT because that too is a horse-crap term. "Toe-tapping" is another. I have one for all these stupid terms; "cringe-worthy". 
Thelonious Monk is known to have said, "writing about music is like dancing to architecture". The same can be said for trying to describe attributes of audio gear but since we gear-heads love to read and write about our hobby, here we are. 
In this age of the internet, there is a democratization of audio reviewing. We have webzines like 6Moons and Parttimeaudiophile in which the level of writing/reviewing is a whole step down from the likes of Mike Fremer, Art Dudley and Jon Atkinson and then below the webzines we have "the 600 lb fat guys living in their mom's basements" putting up whatever they want on this Board and others. And no, the reference to 600lb fat guys is not meant literally, it means some anonymous person who could be anywhere with little or no meaningful knowledge or experience. 
I have multiple hobbies and gravitate to multiple forums/boards. On each, one has to rifle through a ton of chaff to find any wheat.