Okay, so you know when you sing "Row, row, row your boat" with your friends, sometimes you each sing the same thing but start at different times? That's called "polyphony," which means "many voices."
Micropolyphony is when a bunch of different sounds are put together and layered so that they blend together in really cool ways. It's like when you mix different colors of paint together to make a new color.
But instead of colors, it's sounds! And the sounds are really, really, really small - so small that you might not even notice them on their own. But when you listen to them all together, they create a big, beautiful sound that changes and evolves over time. It's like a musical puzzle that grows and changes as you listen to it.
And some really smart musicians, like a composer named Gyorgy Ligeti, liked to use micropolyphony to make music that sounded really different and interesting. They would take a melody, break it up into tiny little pieces, and put each piece on a different instrument or voice. Then they would layer all the sounds together, and it would sound like a big, swirling mass of sound that could change and grow in really cool ways.
So that's micropolyphony - it's like mixing lots of tiny sounds together to make a big, beautiful sound that changes over time. And some really cool musicians like to use it to make really interesting music!