Q
Quarter note (US)
A crotchet

Quartet
A piece for four performers
Quasi
Almost, as if
Quaver
Half a crotchet, an eighth of a semi-breve
Quintet
A piece for five performers
R
Rallentando
Slow down gradually
Re
The second note in sol fa
Renaissance
The period circa 1450-1600
Retenu (Fre)
Slowing down
Ritardando
Slow down suddenly
Ritenuto
Slow down suddenly
Ritmico
Rhythmically
Rondo
A musical form consisting of 5 sections, usually designated A B A C A
Round
Like the canon, a song in which two or more parts having the same melody, starting at different points
Rubato
Flexibility of tempo to achieve expressiveness
Ruhig (Ger)
Calmly