Okay, kiddo. So you know how sometimes when you watch TV or use your computer, there are ads for different things? Well, one of those ads is called "Daisy". It's a TV ad that was made a long time ago, in the 1960s.
The ad shows a little girl picking petals off a daisy flower while counting, and then suddenly the video shows a big, scary explosion. It was trying to make people scared about the possibility of a nuclear war.
People were really worried about nuclear war back then because two big countries, the United States and the Soviet Union, were having problems with each other. The ad was trying to make people think about how dangerous this could be and maybe encourage them to take action to prevent it.
Although the ad is old, people still talk about it because it was so powerful and memorable. Some people think it helped to calm down tensions between the US and Russia. That's why they still show it in some history classes today.