Orchestral percussion is a fancy term for the instruments you will find in an orchestra that are hit or struck to make sounds. These instruments include things like drums, cymbals, triangles, and maracas.
Each of these instruments has its own specific sound and it's the job of the percussionist to play them in a way that complements the music being performed. For example, if the music calls for a loud and powerful sound, the percussionist may play the bass drum or a set of timpani drums. If the music is a bit softer, the percussionist may play the triangle or a set of chimes.
The way the percussionist hits the instrument also makes a difference in the sound it produces. For example, if you hit a cymbal with a soft mallet, it will make a gentle tinkling sound. However, if you hit it with a drumstick, it will produce a loud crashing sound.
Overall, orchestral percussion is an important part of an orchestra as it adds depth, dynamics, and texture to the music being performed. It's a lot of fun to play as there are so many different instruments and ways to create different sounds.