Have you heard of Egypt? It's a big country with lots of people and history. Well, there's a group of people in Egypt called the Copts. They have their own language and traditions that are different from the rest of the people in Egypt.
Coptic nationalism means that the Copts are proud of their culture and want to protect it. They want to make sure that their language and way of life doesn't disappear.
Sometimes people in Egypt treat the Copts unfairly or don't give them the same opportunities as everyone else. So, Coptic nationalists want to fight for their rights and make sure they're treated fairly.
Think of it like if you were really proud of your family's traditions and wanted to make sure they were kept alive even if other people didn't understand or like them. That's what Coptic nationalists are doing, but with their entire culture.