Pedal (music)
Pedal timpani are timpani with a pedal which will tighten or loosen the drumhead.  This will make the note go up or down in pitch.  It is a fairly new invention.  Composers in the Classical music period never had pedal timpani.  Their timpani always had to be tuned by hand using the taps around the side.  Composers like Béla Bartók wrote for pedal timpani.