ELI5: Explain Like I'm 5

Definable number

Hey there kiddo! Do you remember what numbers are? They're like, 1, 2, 3, 4, and so on! Well, did you know that there are some numbers that we can't really write down with just these simple numbers? These are called "indefinable" numbers, because we don't have a simple way of explaining what they are.

But, there are also numbers that we can define using math equations! These are called "definable" numbers. They might be a little harder to understand than just regular numbers, but it's cool that we can actually write them down and figure out what they are!

For example, have you heard of π (pi)? It's a number that we use in math a lot, but we can't just write it down as a regular number. Instead, it's defined by an equation: the circumference of a circle divided by its diameter. This means that we can figure out what π is by doing some math!

So, a "definable number" is a number that we can explain and write down using math equations. It might not be as easy as just counting to 10, but with some math knowledge, we can figure out what these numbers are!