In singing, this refers to a soprano or tenor voice type of a vocal weight between a lyric voice and a dramatic voice, a "light heavyweight" voice.
Lyric voices are light, smooth, sweet, and agile; dramatic voices are heavy, rich, powerful, and full of emotion.
"Spinto" is Italian for "pushed" (this should not imply force) and applied to a tenor or a soprano it means a lyric voice which can be "pushed" to large musical climaxes at moderate intervals. This effect is achieved by a sharp edge in the voice's tone (squillo), which allows it to "cut" through a full orchestra (rather than singing over it like a true dramatic voice).
Since spinto voices bridge lyric and dramatic voices, they are able to play a wide range of roles in opera (but a spinto is not a common voice type).
A spinto tenor or spinto soprano may or may not have a darker color than their lyric counterparts; they often have the color of a baritone/mezzo-soprano and the high tessitura of a tenor/soprano.
Famous operatic spinto sopranos and spinto tenors include Renata Tebaldi, Leontyne Price, Michele Crider, Aprile Millo, Renata Scotto, Mario Lanza, Mario Frangoulis, Carlo Bergonzi, Placido Domingo, and Franco Corelli.
Pop singers who could qualify include Kelly Clarkson, Michelle Branch, Rachelle Lampa, Diana DeGarmo, Adam Lambert, Adam Pascal, Clay Aiken, Freddy Mercury, Steven Tyler, and Michael Jackson.
Loud, or 'pushed, singing. Easily singing forte and above in volume. Usually noted by much dramatization, force, and emotion.
Jennifer Holliday is a spinto singer.