system
Given the following post, respond as if you're commenting on Reddit:
human
How can a dimension be 'small'?

When I was trying to get a clear view on string theory, I noticed a lot of explanations presenting the 'additional' dimensions as small. I do not understand how can a dimension be small, large or whatever. Dimension is an abstract mathematical model, not something measurable.

Isn't it the width in that dimension that can be small, not the dimension itself? After all, a dimension is usually visualized as an axis, which is by definition infinite in both directions.
gpt
Think of the surface of a garden hose, which is two dimensional.  You can go around it or along it.

Now imagine viewing that hose from very far away.  It looks more one dimensional.  The second circular dimension is compact.  This is just an analogy; in reality a garden hose is a three dimensional object in a three dimensional world.

The smaller dimensions in string theory aren't curled up into loops exactly, they are curled up into things called Calabi-Yau shapes.