If you hoard things—like food, or money, or all the best paint colors in art class—that means you get those things and keep them for only yourself in a hidden place. You don't share them. And that big pile of stuff is your hoard.
Here's a squirrel hoarding some nuts. He's going to hide them away so he can eat them later.
People who hoard useful supplies in real life, like food or toilet paper, might be scared or just selfish. They want to use those things for themselves, not just right now but also in the future. During the COVID pandemic, some people hoarded toilet paper because they were afraid of running out.
And people who hoard useless things, like old newspapers, have a big problem. They feel like they must keep all of those things, and sometimes, their piles of stuff get so big and dirty that their lives become very difficult.