What type of vocal technique involves holding a note for an extended duration, often giving emphasis to that note?

The correct answer is sostenuto. This vocal technique refers specifically to holding a note for an extended duration, allowing the singer to emphasize that particular note. Sostenuto can create a sense of gravity and depth within a piece, as it enables the performer to sustain the tone while often adding expressive qualities to the music.

Legato, while related because it involves smooth and connected notes, does not specifically indicate the holding of a note for a longer period. Instead, it refers more to the overall technique of smoothly connecting multiple notes together without noticeable breaks.

Forte refers to loudness in dynamics, indicating how forcefully a note or passage should be played or sung, rather than focusing on the duration of individual notes.

Staccato describes a style of playing or singing where the notes are performed in a detached or separated manner, shortening their duration rather than sustaining them.

Thus, sostenuto is the term that accurately captures the essence of emphasizing a held note within a performance.