Percussion instruments are split into two categories: tuned and untuned.
Tuned percussion covers percussion instruments which can be tuned to particular notes. The most obvious examples are the glockenspiels and xylophones we use in class. The bars on a xylophone are wooden, whereas a glockenspiel’s bars are metal. They are laid out in the same format as a keyboard and played by striking each note with a beater. Vibraphones and marimbas are variations of the same concept.
Timpani are a rare of example drums that are tuned to specific notes. Also known as kettle drums, timpani are large drums with a single skin on top. They have a foot-pedal which is used to raise the pitch when pressed, allowing them to change to different notes mid-performance.
Untuned percussion everything else that is played by striking it, but that doesn’t play a particular note. For example, the 3 toms you would find on a drum kit are pitched at high, medium and low, but as they are not tuned to specific notes, they count as untuned percussion.