system
Given the following post, respond as if you're commenting on Reddit:
human
What is a curled up dimension?

I know this is a stupid question but it’s been bugging me. 

One explanation of the extra dimensions needed for string theory is that they are “curled up.” I can’t make any sense of that. In my mind no matter how small or curled up a dimension is it’s still length or height, just .00000whatever of the same dimension. 

Thanks in advance.
gpt
Imagine a squirrel walking on a telephone wire. To them it seems one dimensional. They only go forwards and backwards. But the wire is actually a cylinder, so something small enough, like an ant, could actually walk in two dimensions around the wire.  The second dimension is curled so small that the squirrel doesn’t know it’s there.