Pollution in China means that the air, water, and land in some parts of China are not very clean. Imagine if you were eating dinner and someone poured dirt all over it. You wouldn't want to eat it anymore, right? The same thing happens in China. The air has a lot of smoke and chemicals in it, the water is not so clear and has a bad smell, and the land has a lot of garbage and chemicals too.
Many people in China use cars and factories that make things like toys, clothes, and electronics. These things make a lot of pollution because they use a lot of energy and produce a lot of waste. Sometimes, people also burn things like garbage or crops, and this makes the air even dirtier.
The pollution in China is not good for people's health. It can make people cough and feel sick. Sometimes, it can even cause more serious problems, like heart disease or cancer. That's why the government is trying to make some rules to reduce pollution. For example, they might tell factories to use cleaner energy or tell people to use public transportation instead of driving.
In short, pollution in China is when the air, water, and land is not clean because of cars, factories, and burning things. It is not good for people's health and the government is trying to make it better.