Okay, so have you ever played with a drum or shaken a pair of maracas? Those are examples of untuned percussion.
Untuned percussion instruments are ones that don't have a specific pitch like a piano or guitar. Instead, they make sounds that are more about rhythm and adding texture to music.
Some other examples of untuned percussion you might see or hear in music are the tambourine, bongos, and cowbell. They can be hit, shaken, or even scraped to make different sounds.
So basically, untuned percussion is all about making cool noises that help make music more interesting and fun to listen to!