single word requests - What do you call a disk with a hole in the middle?


Compact Discs, washers and Aerobie frisbees are all disks with a hole in the middle. Is there a word (either mathematical or not) to describe this shape? I mean the specific case of a round hole in a flat disk such that the inner and outer rings are concentric circles, like below.


Some Disks with holes in the middle


--Edit: Accepted answer


I feel rather unqualified to select one answer as correct, so I'm going to choose the one that says "It depends who you're talking to". I hope that future readers will choose between the various helpful answers here depending on their exact object and their audience. After reading the etymology of annulus, I also hope that nobody ever tries to market an "Incredible Flying Annulus" to 13-year old boys.



Answer



There is an informal, nontechnical-English answer and a technical mathematical answer.




  • informally, it can be a ring (like a coffee ring, aerobie, or washer (the last one is questionable, could be 'washer-shaped'), or a disk or disk with hole in it for compact disk (because the hole is somewhat secondary).




  • technically, it is an annulus.




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