Have you ever heard of a website? It's a place that you can go on the internet to learn or play games or look at pictures. When you go to a website, you usually have to type in the name of the website that you want to go to.
Now, imagine if every website had to end with a certain word, like ".com" or ".org". That is called a top-level domain. It's the part of the website name that comes after the dot.
There are different kinds of top-level domains. "Com" is one of the most common ones and it stands for "commercial". It's used by businesses that sell things or provide services. "Org" stands for "organization" and it's used by groups that want to do good things, like charities or non-profits. There are also top-level domains for different countries, like ".ca" for Canada or ".uk" for the United Kingdom.
So, when you type in a website address, you're really typing in the name of the website, followed by a dot and a top-level domain. It's kind of like a secret code that helps the internet know where to send you when you want to go somewhere on the web.