Intonation is basically pitch, but it's more than that especially with the voice. It's how the pitch is presented, and in voice, how the tonal part of the word is sung. In linguistics, intonation is the variation of the spoken word not used to distinguish the words themselves, but instead indicate an attitude or an emotion of the speaker. You've probably seen examples of an actor saying the same line several times, each with a different inflection, or intonation, changing the meaning or emotion of the sentence. One of the more famous and funny examples is the 1979 SNL skit with Steve Martin and Bill Murray.
So it's an emotion and how the phrasing is presented. If you watch "The Voice" on TV during the coaching sessions, you'll see how the teach singing different words or phrases with a more guttural, raspy, or more or less powerful voice, depending on what the words are saying and the emotion involved. Phrasing also means breathing in the right place. You don't want to take a breath in the middle of a word or phrase, because the music then sounds disjointed and the emotion and the story the words are telling is lost.
You want to sing,
"O beautiful for spacious skies, for amber waves of grain" all in one breath, because that's the phrasing of the music without the words.
You don't want to sing it as,
"O beautiful <gasp>
for spacious skies <gasp>
for amber waves of grain," even though some people do it, because it sounds retarded.
To get phrasing and intonation right in pop music is hard enough, but in opera it's a very difficult thing to do even for accomplished professionals. That's why the top opera singers around the world still employ vocal coaches year around.
When this kid sings, she looks, and sounds, like she's got a lifetime of experience and emotion coming out through those words.
The aria is from Puccini's opera
Gianni Schicchi. It is one of the shortest, and arguably the most emotional of all the arias in opera. It is sung in the opera by the character Lauretta after tensions between her father Schicchi and the family of Rinuccio, the boy she loves, have reached a breaking point that threatens to separate her from Rinuccio. The opera is a comedy, but the atmosphere is rife with hypocrisy, jealousy, double-dealing and feuding set medieval Florence. The aria is performed by many sopranos as an encore, and is performed far more often than the opera itself. There are dozens of different YouTube videos of "O mio babbino caro" by some of the greatest singers alive and dead.
The English translation of the lyrics (O my beloved father):
Oh my beloved father,
I love him, I love him!
I’ll go to Porta Rossa,
To buy our wedding ring.
Oh yes, I really love him.
And if you still say no,
I’ll go to Ponte Vecchio,
And throw myself below.
My love for which I suffer,
At last, I want to die.
Father I pray, I pray.
Father I pray, I pray.
