Okay kiddo, so you know how when you have a bunch of toys and you keep them all in one place, like a toybox? That's kind of like a collection. A collection is when you have a group of things that are similar in some way and you keep them all together in one place.
Now, let's imagine that instead of toys, we have books. And instead of a toybox, we have a bookshelf. If someone has a lot of books about cats, they might want to keep them all together on one shelf. That way, if they want to read a book about cats, they know just where to look.
When people make books, they often want to make a collection of their work. For example, a poet might write lots of poems over the years, and they might want to collect all their best ones in one book. Or a photographer might want to make a book that has all their favorite photos in it.
When someone makes a collection of their work like this, they can publish it. That means they make lots of copies of the book and send them out to stores so people can buy them. So if you like a particular author or artist, you might see a book that has all their best work in it and decide to buy it.
So that's what a collection is in publishing: it's a book that brings together a group of similar things (like poems or photos) in one place, and that book is then published and sold in stores for people to enjoy.