What is "sostenuto"

Sostenuto \Sos`te*nu"to\, a. [It.] (Mus.) Sustained; -- applied to a movement or passage the sounds of which are to sustained to the utmost of the nominal value of the time; also, to a passage the tones of which are to be somewhat prolonged or protacted.

adv. (label en music) played in a sustained manner beyond the notes normal value n. A note or passage marked to be sustained

In music, sostenuto is a term from Italian that means "sustained". It occasionally implies a slowing of tempo, though more often it refers to a very legato style in which the notes are performed in a sustained manner beyond their normal values.