Small Start, Big Finish

"''"Once in every show, there comes a song like this

It starts off soft and low, and it ends up with a kiss

Oh, where is the song that goes like this... where it is? Where? WHERE?

A sentimental song that casts a magic spell

They all will sing along, we'll overact like hell

Oh, this is the song that goes like this. Yes it is. Yes it is! YEEESSSS IT IIIISSSSSS!"''"

- Spamalot, "The Song That Goes Like This"

Exactly What It Says On the Tin. This is a type of musical number which, naturally, has a small beginning and a big ending. These are usually done by one character in a solo, a solo verse in a duet continuing on to the end, or sometimes the lead part in an ensemble number. It may occur in a musical or just an atmosphere where there's music. Usually done with celebrities or just people who are famous for their singing, since anyone who knows them knows they can sing; they're just waiting for that one money-making note. It can usually occur in one of four forms:

Type 1:
Alice is very talented but shy. She wants to perform, but she's never sung in public before. She's already gotten the courage to get into whatever show she's in. She's practiced her ass off. Now it's time to perform in front of a huge crowd. She starts small and not confident but slowly becomes more sure of her own singing. Before she gets to the end, she's already pulled a Show Stopper.

Type 2:
Bob is timid and has yet to come out of his shell. Finally during one of his musical numbers he makes a breakthrough. He starts out small and shy, just being himself, until he finally comes out. By the end of the song, he is belting at full-force. He will probably win an award for this performance.

Type 3:
Usually occurs in non-musicals (i.e. movies or TV shows with a lot of music; That Reminds Me of a Song moments) Claire has a perfectly good voice. She's not ashamed of it, nor is she afraid to sing in public. She just doesn't use it. We've known her long enough that we think we know her real personality. Suddenly, for whatever reason, she will start singing (usually when nobody is watching). She will, once again, start small (or at least very soft), and gradually grow. When she reaches the end and we progress to the next scene, everyone is still gaping, thinking "What the hell just happened?" and "I didn't know she could do that!"

Type 4:
Can be used by any type of character, representing the birth and buildup of a single thought. The character starts out with the bud of an idea, which they sing in a smaller voice. As they become more sure of themselves, the song grows. In some cases done with an ensemble in the background.

Types 1-3 are usually worthy of a standing ovation because they show a character doing something we didn't necessarily know they could do. Type 4, however, is more often used by characters we already knew could sing.

Film

 * Done with Gabriella in High School Musical, though less skilfully because we already knew she had talent. So it wasn't much of a surprise when she came out.
 * Mary from Superstar has one of these, although sort of subverted because she does screw up terribly in the middle before she gets back on her feet. And because, well, Molly Shannon isn't exactly a singer.

Live Action TV

 * In an episode of the short-lived series What About Joan, Donna Murphy does it beautifully.

Theater

 * Louise's life-changing rendition of "Let Me Entertain You" from Gypsy.

Film

 * At least speaking for the film version, this happens to both Seymour and Audrey during "Suddenly Seymour" in Little Shop of Horrors. Of course it all depends on performance (Ellen Greene pretty much plays this trope straight, whereas Kerry Butler seems to let loose a earlier in the show).

Theater

 * "If I Were A Bell" from Guys and Dolls is an interesting example; Sarah does indeed come out of herself, but she's drunk the entire time.
 * Hairspray's Penny Pingleton has an incredibly short one during her part in "Without Love."

Film

 * In the remake of Fame, Denise doesn't sing in the movie at all until later, when she sits at the piano and delivers this trope. It may be one of the only memorable performances from the movie.

Live Action TV

 * The first episode of Pushing Daisies where Vivian (Ellen Greene) sings definitely counts. The number doesn't really get bigger, per sé, but it does get louder.
 * Also when Olive (Kristin Chenoweth) sings "Hopelessly Devoted To You," even though people keep interrupting her.
 * Speaking of Kristin Chenoweth, her performance of "Maybe This Time" on Glee also counts. Of course, we were all waiting to hear the high note at the end.

Theater
Get ready.
 * A great deal of the songs from Rent.
 * Being Alive.
 * Defying Gravity.
 * My Own Best Friend and Nowadays.
 * Maybe This Time.
 * You'll Never Walk Alone.
 * In some respects, "Ain't It Good" from Children of Eden.
 * "You Can Always Count on Me" and "Funny" from City of Angels.
 * "I'm Still Here," from Follies. Except possibly Elaine Stritch's rendition. After all, she's Elaine Stritch.
 * The reprise of Don't Rain on My Parade.
 * Gimme Gimme.
 * I Know Where I've Been.
 * Last Midnight.
 * I Am What I Am.
 * As Long As He Needs Me.
 * Kristin Chenoweth's A House Is Not A Home. At least near the end.
 * Johanna
 * Living in the Shadows
 * "Before the Parade Passes By" and the title song from Hello Dolly.