De-industrialization means that the big factories and manufacturing plants that used to make a lot of stuff are shutting down and leaving town. It's like when your favorite toy store closes down and you can't go there anymore.
This happens for different reasons, but one big reason is that companies can find cheaper places to make their things. So, they might move to another country where workers get paid less money to do the same work. Or, they might start using machines to build things instead of people, which means they don't need as many workers anymore.
When the factories and plants close down, a lot of people lose their jobs. This can make it hard for them to pay for things like food and rent. It can also make it hard for the town to make money and grow because there aren't as many people working and buying things.
De-industrialization can be a big change for a town or even for a whole country. But sometimes, new opportunities come up that can help people learn new things and find new jobs. So even though it can be hard, change can also mean new beginnings.