Imagine you are naming your toy box to keep all of your toys organized. You write "TOYS" on the box so you know that's where they belong.
Now, imagine you want to do the same thing but for a website. You need to come up with a catchy name that people will remember so they can find your website easily. This is called a domain name.
Domain name warehousing is when someone buys a lot of different domain names and holds onto them like a toy box, instead of using them right away. They hope to sell them later for more money to people who want a good domain name.
It's like if you were to buy many different toy boxes, each with a different toy name on it and not use them for anything except selling them later for more money.
Some people think domain name warehousing is a bad thing because it makes it harder for people to get good domain names for their websites. But others think it's just like any other type of investment, and can be a good way to make a profit.