Rushing and dragging

When performers unintentionally speed up, they are said to rush . The similar term for unintentionally slowing down is drag .
Unless practiced by an experienced performer to achieve a particular musical effect, these actions are undesirable; dragging can often indicate a hesitance in the performer due to lack of practice; rushing can likewise destroy the pulse of the music.
Because of their negative connotation, neither rush nor drag  (nor their equivalents in other languages) are often used as tempo indications in scores, Mahler being a notable exception: as part of a tempo indication he used schleppend  (dragging) in the first movement of his Symphony No. 1, for example.
By practicing with a metronome a musician can try to gain control over rushing or dragging.