Just a note to the readers on my opinion of talent. Being able to sing, that is talent, but for a musical artist, being able to sing to me is just a prerequisite of being able to do for a living. If you can't sing, you can't do what you do for a living, unless you sell yourself through means of sex. In that case you aren't a talent, just a pretty face (or muscular man, whatever). So what then is talent in the 'music' industry?

A standard piano has 7 octaves. Mariah can sing 5 of them. That is talent.
Being able to produce, co-produce, read/write music. That is talent.
If you can't WRITE music, then because you are just a plain ol' singer. Lyrics don't count, though if you had great lyrics it helps.
If you can play an instrument well, while singing well. That is talent.

If you can dance and sing, then that is half-talent. You can learn to dance, so it's not so much talent but a skill, but being able to sing well while dancing is not easy, so that is talent. Of course dancing has nothing to do with music, in my opinion. Dancing is just an MTV thing, if there were no music video's, no one would care if you could dance or not. In fact, the only reason I think these teeny boppers dance is because they'd look stupid just standing there singing, especially when they can't even sing that well. At least if they're dancing, they can use that as an excuse to not being able to sing well. Obviously singing is the most important thing.

Keeping in mind talent is all relative. We're talking about artists in the music industry so there's a certain level of expectation there:

Let's say there is a scoring system for talent level. Note this is just based on Talent. Obviously some people like artist who look better, or just simply don't like a particular style of music.

0-15 : Ability to sing
7.5 pts : Ability to write/produce/co-produce* own music
7.5 pts : Ability to play an instrument

So, someone like Eric Clapton would score 30/35. Not the greatest voice, but he is unbelievable on the 6-string, and writes his own stuff.
Mariah Carey would score 21/30. Alicia Keys, 30/30.. Alicia is really talented.. Songs in A minor was an awesome, awesome album, though not really 'pop'-ey, so probably didn't sell as well as it should have. Christina Aguilera gets 18/30. Britney Spears gets 10/30. Most bands (not groups) score perfect, because they've got singers, guitarist, and a drummer. They cover it all -- What they play is what you hear.

In a nutshell, that last sentence covers what I define as musical talent - What they play is what you hear. If they produced everything that you are hearing, not just the vocals, but the instrumentals, or the backup vocals, then THAT is talent.

*I'm not totally positive on this, but I think producing music is listening to and mixing samples, kinda like what Jermaine Dupri, or Sean Combs does. Well, sampling is probably more related to their genre of music, whereas someone like Jimmy Iovine just listens to the music he's given and then just picks what he likes. It sounds like a pretty cool job, but probably takes a tremendous amount of pressure, since they are hired to compile the best album possible, and are hired by the artists themselves.. so if the artist is able to produce their own stuff, that must also take a lot of work, because when you're sifting through your own stuff, it must be pretty hard to decide what is crap and what is good..