Okay kiddo, so imagine there are two groups of people who don't get along - let's call them Group A and Group B. Sometimes, the people in Group A might do things that are really, really bad and dangerous. They might try to hurt or kill the people in Group B, or they might blow up buildings or do other terrible things.
When this happens, the government (which is like the grown-up in charge of making sure everyone is safe) might decide that the people in Group A are "enemy combatants." That means they're not just regular people who made a mistake - they're like soldiers who are fighting a war against Group B.
When someone is labeled an enemy combatant, it means they're not going to be treated the same way as other people who break the law. Instead of going through a regular legal process like going to court, they might be held in a special place like a prison or detention center. This is because the government thinks they're really dangerous and might do more bad things if they were let go.
Now, some people don't like the idea of enemy combatants. They think that everyone should be treated the same way under the law, whether they're in Group A or Group B. Some people also worry that if the government is allowed to call someone an enemy combatant without having to prove it in court, they might start calling lots of people enemy combatants for not-so-good reasons.
So, that's what an enemy combatant is - someone who is seen as a soldier fighting in a war against another group, and who might be treated differently under the law because of it.