Musical pieces that don't have any lyrics or singing are called instrumental pieces.
The musical term for a singing voice that vibrates is vibrato. It is produced by rapidly changing the pitch just slightly.
Musical numbers is just another term for song.
A musical group of seven is a "septet."
Do you mean for six people playing and/or singing together? That is a sextet.
A capella A cappela
You are probably thinking of "syncopation".
ballad
The Sound of Music in the song "Maria"
Refrain
Although often spelled as one, the singing term is two words a capella (without musical accompaniment).The phrase is Italian for "as in church."
"Cantabile" in music refers to a smooth and lyrical style of playing or singing. It emphasizes the expression of melody with a singing quality. This term influences the overall interpretation of a musical piece by guiding performers to focus on creating a flowing and melodious sound, enhancing the emotional and expressive aspects of the music.
"Melisma" is the term used for singing of a single syllable over a succession of musical notes. This singing style is called melismatic.