A company is like a big group of people who work together to sell things or provide a service. When a company is publicly traded, that means the company's shares (or pieces) are available for anyone to buy and sell on the stock market. But sometimes a company doesn't want to be publicly traded anymore, so they decide to become a publicly unlisted company.
Think of it like a club that used to be open to anyone, but now only people who are invited can join. When a company becomes publicly unlisted, they no longer sell shares on the stock market and their financial information and secrets are kept private. This makes it harder for anyone outside the company to know what they're doing with their money.
Some things might happen when a company becomes publicly unlisted. They might have more control over their own decisions because they don't have to listen to as many people who own a piece of the company. They might also be able to take more risks with their money or make big changes to their business without worrying so much about what the stock market thinks. But they also might not be able to get as much money by selling shares, and they might not be as well-known as they used to be.