What is Special About Dimensions of Physical Space?

In my recent Worlds of 1 Spatial Dimension article, I wrote about various one-dimensional worlds (the Income Line, the Rainbow Line, and the Aeolian Line) — all of them involving dimensions which are not themselves physical dimensions of space. What is the distinction between a general dimension and an honest-to-goodness spatial dimension? In short, what do we mean by saying that a dimension has something to do with physical space?   Click here to learn more.