Ordinal definable set
Okay kiddo, an ordinal definable set is a group of things that can be described using a system of numbers called ordinals.
Think of it like a bunch of toys in a toybox. Each toy has a number assigned to it, starting with 1 and going up from there. The first toy has the number 1, the second toy has the number 2, and so on.
Now imagine that there are certain toys that can only be described by using these ordinal numbers. So if you wanted to talk about the third toy in the box, you would use the ordinal number 3 to describe it.
A set of toys that can only be described using these ordinal numbers is called an ordinal definable set. It's like having a special group of toys that can only be talked about in a certain way.
So, to sum it up, an ordinal definable set is a group of things (like toys) that can only be described using a special system of numbers called ordinals.
Think of it like a bunch of toys in a toybox. Each toy has a number assigned to it, starting with 1 and going up from there. The first toy has the number 1, the second toy has the number 2, and so on.
Now imagine that there are certain toys that can only be described by using these ordinal numbers. So if you wanted to talk about the third toy in the box, you would use the ordinal number 3 to describe it.
A set of toys that can only be described using these ordinal numbers is called an ordinal definable set. It's like having a special group of toys that can only be talked about in a certain way.
So, to sum it up, an ordinal definable set is a group of things (like toys) that can only be described using a special system of numbers called ordinals.