So, you know how when you type in a website, like "www.google.com", you see a bunch of words and symbols? That's called a domain name. It's like the website's address, so your computer knows where to go to find that website.
Now, sometimes people decide they don't want their domain name anymore for different reasons, like they might not be using it anymore, or they might not have enough money to keep paying for it. When that happens, they let it go and it becomes available for someone else to use.
The domain name drop list is a big list of all the domain names that people have let go, and it's a place where people can go to see which ones are available to use. It's like going to a sale to see what toys are left that nobody wanted, but now you can take them home and play with them.
But, just like a sale, you have to be quick to grab the domain name you want, because other people might also be looking at the same list and trying to grab the same domain name.