A circle or a 2-D projection of a starfish is considered "radially" symmetric. I am wondering what is the terminology for radial symmetry such that the distance from the center of the 2-D shape and its boundary is the same everywhere as in the case of a circle, but not the starfish.
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If I understand your question, it sounds like you're asking for a special word/phrase for "being a union of concentric circles in the plane" (or "having a circle as its boundary"? Or maybe "being a disk"?), and I doubt there is one. – Mark S. Oct 21 '20 at 01:50
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1@MarkS. I did some googling, and I think perhaps I'm looking for the term "n-sphere" or "n-ball" although I'm not sure what the distinction is. – user5965026 Oct 21 '20 at 02:04
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I'm not so sure. If you had asked "What do we call something like a circle in higher dimensions" or not said "the 2-D shape", then one or both of those ("n-sphere" and "n-ball") might be a good fit. But since your question seemed focused on 2D shapes (in the plane?), and you phrased things in terms of symmetry, it seems like those might be what you're looking for. – Mark S. Oct 21 '20 at 11:37