Okay kiddo, so sometimes grown-ups work to earn money, and usually they work for about 8 hours a day, right? Well, some people think that's too much time to spend working and they believe that grown-ups should only work for 7 hours a day instead – and that would be 35 hours a week total.
Now, some places in the world already have this rule – it's a law, which means everybody has to follow it. It means that grown-ups get to spend more time doing other things they like or need to do, like taking care of their home, spending time with family and friends, or even resting so they can be healthier and happier.
But other places in the world don’t have this law yet, so people might work longer hours every day, or work longer weeks. Some people think that’s not good because it can make grown-ups very tired, stressed, and even sick. That's why they want a 35-hour workweek.
So, the 35-hour workweek is just an idea that means grown-ups would have a little more time to do other things in their life instead of working a lot. Sounds nice, doesn't it?