Hello there! Megali Idea is a term used to describe a big idea that people in Greece had a long, long time ago.
Now, let me explain it to you like you're five years old, okay?
Back then, Greece was a big empire that ruled over many lands and people, but over time it became smaller and weaker.
The people of Greece came up with this big idea called the Megali Idea. They wanted to make Greece big and strong again! They wanted to bring together all the Greeks who lived in different countries and form a big country of their own.
They wanted to expand Greece's borders and claim lands that were once part of ancient Greece, such as parts of Turkey, Albania and Macedonia.
The Megali Idea was very important to the people of Greece because they wanted to be a proud and powerful country once again.
However, not everyone agreed with the Megali Idea and some countries didn't want to give up their lands. This caused some conflicts and wars, but Greece never gave up on their big idea.
And that, my dear, is a brief explanation of the Megali Idea – a big idea that people in Greece had to make their country bigger and stronger.