I'm NOT asking you who's a musical genius and who isn't. I just want to hear your own definition of it.

Discuss.

Someone who makes really good music that is filled with unique, creative, and original ideas.

So someone like Prince.

Basically all of this, you could say that someone like Madeon is a genius in his area of music. He's only 18 and can create so many amazing songs

Originality and innovation for the most part but It also depends on personal taste to some extent.

People like Marina and the Diamonds who are superb in every field.

I would have to agree here. They have to be and interesting and talented artist who is capable of creating a real spectacle as opposed to the same old stuff you hear everyday. Musical "geniuses" seem, to be honest, to be becoming more and more rare each passing generation; not because there are less of them, but because the mainstream is becoming more and more focused on popular trends. A true musical genius is less likely to break through and be seen nowadays, I think.

Katy Perry.
Edit: Oh, didn't see the OP correctly. Well, Katy represents the qualities one musical genius must have.

Innovative, game changing.

Musical originality, creativity
Songwriting, musicianship
How it compares to others within the genre

This. But would you say that being groundbreaking is also a prerequisite to being a musical genius? Because just about every artist widely considered a musical genius revolutionized music in some way.

Jonny, please don't be one of those annoying stans.

Yes, I would. But being creative/original/innovative sort of goes with that.

No one in the pop mainstream right now, that's for sure. They're all radio-catered factory machines we feed off of.

Someone who brings an entirely new genre, trend, or a new twist to a pre-existing genre. Pioneers of a new genre

In Some way or another. But it depends on what you mean by groundbreaking. Nirvana didnt break any ground musically, all they did was ape the Pixies, but Kurt is still seen as some sort of genius.

Trend wise, I guess they did break ground in the acceptance of alternative music in the mainstream.

I gagged a little

I agree, and they probably respond to and process music very differently compared to most people.

I was wondering why the music industry has gone to crap, and you pretty much hit the nail on the head.

Their are many forms of a musical genius.

I think one important one is, to not only be able to set trends, but to be able to take the current trends in music and turn them into something greater.

That, and being able to play a lot of instruments with ease.

i think someone is a musical genius if they can do this:

. play instruments extremely well
. are great songwriters
. are really good VOCALISTS, which includes having great range, tone, control among many other things.
. Can explore many different topics within the artists music
. Can incorporate many genres in their music
. Can innovate (not necessarily be the first do it) different sub genres of music

etc.....