Deuxième bureau is a phrase that means "second office" in French. But what does this really mean? Well, imagine you have a secret hiding spot in your room that only you know about. Deuxième bureau is kind of like that - it's a secret place where people can do things that maybe they don't want others to know about.
During World War II, the French Resistance used the term deuxième bureau to refer to their secret intelligence operations. They had to work in secret to gather information without the Nazis finding out. This was really important because if the Nazis found out what they were doing, they could have been captured or killed.
Nowadays, the term deuxième bureau can refer to anything that people keep secret from others. It might be a secret project at work or a secret relationship. The idea is that it's something you don't want others to know about, just like the French Resistance didn't want the Nazis finding out what they were up to.
Overall, deuxième bureau is a phrase that refers to a secret place or activity that people keep hidden from others. Just like your secret hiding spot in your room, it's something special that is only for you to know about.