Expression & tempo
Rubato
Rubato is expressive flexibility of tempo, in which the performer stretches some notes and hurries others while the underlying pulse remains recognisable.
The name means "stolen time", and the older understanding is literal: time taken from one note is repaid to another, so the phrase arrives where it would have anyway. The romantic conception is freer, allowing the whole pulse to breathe, but even there rubato only reads as expression when there is a steady pulse for the listener to measure it against.
It is the hardest expressive device to teach and the easiest to overuse. The practical test is whether an accompanist or a section could follow, rubato that no one can play with has stopped being interpretation and become unsteadiness.
Related terms
Every term in this glossary is taught in context somewhere in Arco's curricula, on the staff, on the keyboard, and on your own fingerboard at the same time.