The polyphonic era refers to a time in music history when people started writing pieces of music that had more than one melody going on at the same time. It was like having multiple people singing different things all at once, but somehow it all came together to create something beautiful.
Before this time, music was very simple and only had one melody or tune. But as people began to learn more about music and how to write it, they started experimenting with different melodies and how they could work together. This led to the creation of polyphonic music.
One of the most famous polyphonic composers was Johann Sebastian Bach. He wrote many pieces of music that had multiple melodies going on at the same time, and they are still popular today.
So, basically, the polyphonic era was a time when people started writing more complex music that had multiple melodies happening at once, and it changed the way we think about music to this day.