Okay kiddo, so have you ever seen those movies where the good guys sneak into a bad guy's hideout to rescue someone or steal something? That's kind of like what a "coup de main" is.
It's a fancy way of saying "sneak attack" or "surprise attack", where a group of people plan and carry out a sudden attack on their enemies. The idea is to catch the bad guys off guard and take them by surprise.
Sometimes a coup de main might involve a small group of soldiers or spies who sneak behind enemy lines to take a key position or capture an important person. Other times, it might be a larger group of soldiers who launch a surprise attack on enemy troops.
The thing about a coup de main is that it's all about timing and coordination. Everyone has to work together and move quickly and quietly to make sure they catch the bad guys unawares. It takes a lot of planning and skill, but if it's done right, a coup de main can be a really effective way to win a battle or achieve an important goal.