Okay, so let's imagine you and your friend are playing a game with toy guns in the park. You are on one team and your friend is on the other. Your friend is the "enemy" because you're trying to "combat" each other.
Now, imagine if there was a real war happening where soldiers are fighting against each other. Sometimes, someone fighting for the other team might not be from that team's country. They might be from a different country or not even have a country at all.
Those people are called "enemy combatants." It means they are fighting against the other side, but they might not be officially part of a military or a country's army. It can be complicated to know how to treat these people because they might not follow the same rules as a soldier who is part of a recognized army.
So, in summary, an enemy combatant is someone who is fighting against one side in a war but might not be officially part of a military or country's army.