Rubato

Tempo rubato is a musical term referring to expressive and rhythmic freedom by a slight speeding up and then slowing down of the tempo of a piece at the discretion of the soloist or the conductor. Rubato is an expressive shaping of music that is a part of phrasing.

• the temporary disregarding of strict tempo to allow an expressive quickening or slackening, usually without altering the overall pace.

The term “rubato” should be borrowed from music for what he does here … treating time plastically, like a sculptor does clay ― Codex OS on Twitter