Okay, so let's pretend you're playing a game of make-believe with your friends. You decide to be a superhero and you make up a cool name like "Captain Sparkle." That name is like your superhero name – it's not your real name, but it helps you feel like a really cool superhero!
Well, grown-up soldiers and fighters sometimes do something similar. When they're fighting in a war or doing some kind of dangerous job, they might use a different name that isn't their real name. This name is called a "nom de guerre", which is just a fancy way of saying "war name" in French.
So, let's say there's a soldier named John Smith. But when he's fighting in a war, he doesn't want the enemy to know his real name. So he might use a different name like "Sgt. Fury" or "Rambo" instead. It's sort of like having a secret superhero identity, but for fighting in wars instead of saving the day from bad guys.
Overall, nom de guerre is just another name that someone might use to hide their real identity when they're doing risky or dangerous things.