On this math forum it is implied to be "the distance between circles" as well as "the distance between the circles of the spiral".

A local ByLaw implies the meaning is distance between two places.

I'm looking for a definitive correct interpretation.

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Given some central reference point $A$, the radial separation between locations $X$ and $Y$ is the number of degrees (or radians, if you prefer) in the angle $XAY$.