Imagine you have a lot of toys in your room, so many that you can't keep track of them all. You don't know where you put your favorite toy car or your favorite doll. That's kind of like how Quantcast, a big company that deals with advertising on the internet, used to have a problem with storing all of their important information.
To fix this problem, they created something called a "Quantcast File System" or QFS for short. Think of QFS like a big toy box with lots of compartments, where each compartment has a name or number. Whenever Quantcast needs to store information, they put it into one of the compartments.
But QFS isn't just one toy box, it's actually a bunch of toy boxes all connected together. That way, Quantcast can store even more information, like having several big toy boxes instead of just one.
But what's really cool about QFS is that it can find things really quickly. Imagine you wanted to find your favorite toy car. With QFS, you would just need to remember which compartment it's in, and then go straight to that compartment to find it. This is kind of like searching for something on the internet using a search engine like Google. QFS makes it easy for Quantcast to find their important information quickly and easily.