Tacet is
Latin for "it is silent". It is a musical term to indicate that an instrument or voice does not sound. In vocal polyphony and in orchestral scores, it usually indicates a long period of time, typically an entire
movement. In more modern music such as
jazz, tacet tends to mark considerably shorter breaks. It was common for early
symphonies to leave out the
brass or
percussion in certain movements, especially in slow (second) movements, and this is the instruction given in the parts for the player to wait until the end of the movement.