Prosody is a fancy word that means the way we say and sing words in a special rhythm and tone. It's like how some people talk really fast or slow, or some songs have a happy beat while others are sad.
In Greek, people were really interested in making their words and songs sound nice and important. They called this "prosody." They had special rules for how long or short the different parts of words should be, and how high or low they should be said.
It was kind of like a game to figure out the right way to say things so that they sounded really good! It was also a way to show that you were smart and educated when you could use the right prosody.
Even today, we still use some of these rules when we sing or recite poetry in Greek. It makes the words sound more beautiful and interesting.