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I've asked a lot of questions about disks (example 1, example 2, example 3). There is no tag for disk, so I just choose the circle tag. But the circle tag's description is fairly clear about the scope of this tag: "For questions concerning circles. A circle is the locus of points in a plane that are at a fixed distance from a fixed point".

Should the circle tag's description be modified to include disks?

Update: The circle tag's description has been modified to include disks: "For elementary questions concerning circles (or disks)".

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    $\begingroup$ I have submitted an edit to the tag description. It's not perfect, but I do think it helps clarify the scope of the tag. $\endgroup$
    – Joe
    Jan 29 at 12:26

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I looked through the questions that are already tagged "circle", and most of the questions are about elementary geometry. In my experience, in elementary geometry, the technical distinction between "circles" and "disks" is seldom honoured; indeed, it is much more common to speak of "the area of a circle" rather than "the area of a disk". Thus, it makes sense to note in the tag description that questions about "circles" might well be about disks.

The only worry I have is that disks arise in other, far less elementary, areas of mathematics, such as complex analysis. I don't think it is useful to have questions about complex analysis grouped together with those about elementary geometry, even if they do both happen to involve disks. So perhaps it also makes sense to discourage people in the tag description from using the tag "circle" if their question is about complex analysis rather than elementary geometry.

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    $\begingroup$ In the tag description, the area is referred to as "the area enclosed by a circle", which indicates, at least to me, the distinction is being made in the description. One may be able to phrase a complex analysis problem involving disks, if rather unnaturally, in terms of circle. But of course, that doesn't make it desirable to use the circle tag for the problem. So it seems to me the problem isn't whether we add disk into the tag description, but the tag description not being clear enough to exclude certain contexts. $\endgroup$
    – Divide1918
    Jan 28 at 9:29
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    $\begingroup$ @Divide1918: I see your point. What I meant in my post was that generally speaking, in elementary geometry, we don't fuss about the difference between circles and disks (and I would go as far as to suggest that many schoolteachers are not even aware that there is a difference). I agree that there is not much danger in someone asking a complex analysis problem and tagging it with "circle", but there might be a greater risk if, for instance, we created "disk" as a tag synonym for "circle". Apologies if that wasn't clear from my original post. $\endgroup$
    – Joe
    Jan 29 at 12:13
  • $\begingroup$ Finally, I agree that the tag description should exclude certain contexts, and I am about to suggest an edit now. $\endgroup$
    – Joe
    Jan 29 at 12:14

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