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Imagine a tube, split in half laterally, discarding one of the halves. Does the remaining shape have a name? Like this.

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    $\begingroup$ Like a half pipe? I'd just say half pipe. $\endgroup$ – Jackozee Hakkiuz May 15 at 2:18
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    $\begingroup$ I'd call it a disk. $\endgroup$ – Couchy311 May 15 at 2:28
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    $\begingroup$ It can be called a circular trough. $\endgroup$ – John Douma May 15 at 2:45
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    $\begingroup$ @Couchy311 >implying we allow equivalence under ambient isotopy. Then the homotopy theorist comes and calls it a point smh. $\endgroup$ – Jackozee Hakkiuz May 15 at 2:46
  • $\begingroup$ Are you referring to something like this? I'd like to know as well. $\endgroup$ – ExtremeRaider May 15 at 3:00
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I don't have a formal name for it but circle with a smaller circle cut out of it is an "annulus". Extruding a shape into 3d with a rectangle makes it a prism so the full shape would be "annula-prism" and a half version of the shape would be a "semi-annula-prism".

If the tube is round rather then rectangular (so it looks like a donut) it is a half-torus.

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