What does the underscore mean in literal numbers?

Question

What does that mean?
0.0..10_000.0

Answer 1

Actually all other answers here are wrong.

_ is not ignored, just try it with 0_50:

> 1_50
 => 150
> 0_50
 => 40

YEAAAAAAH YOU WILL FREAK OUT IF YOU JUST WANTED TO USE IT FOR DECIMALS :(

In general it just describes a range of numbers, like CCD mentions above.

As Kyle Heironimus commented, the underscore is actually ignored.