Keyspace is like a big box that holds a lot of small boxes inside it. Each small box has a special name on it, like a label. When we want to find something inside the big box, we look for the small box with the special name on it.
In a distributed data store, there are lots of these big boxes, each one holding different small boxes with their special names on them. Sometimes, we need to find something inside one of these big boxes, but we don't know which small box it's in or which big box it's in.
To help us find what we're looking for, we use something called a key. A key is like a special word that tells us which small box to look for inside which big box. Each key is unique, so we know that we'll only find one thing when we use a key to search.
So, keyspace is just a fancy way of saying "all the big boxes with their small boxes inside, and all the special words that tell us which small box to look for." It's a way to organize and keep track of lots of different pieces of information in a distributed data store.