A partially ordered set is like a big box of toys where each toy has a certain relationship with another toy. Some toys might be big and some might be small, but they can all be compared to each other in terms of size.
But there are some toys that can't be compared in terms of size, because they aren't the same kind of toy. For example, a toy car and a stuffed animal can't really be compared in terms of size.
In a partially ordered set, there are some things that can be compared to each other, and some things that can't. It's like a list of things, where some things are above others and some are below, but there's no way to say that one thing is "better" than another thing.
For example, imagine a list of animals. We could say that a zebra is above a worm, because it's bigger and more complex. But we can't say that a zebra is "better" than a worm, because they both have their own unique qualities.
So a partially ordered set is a way of organizing things based on how they relate to each other, without making value judgements about which thing is better or worse.