# What is the name of a part of a region between concentric circles?

I am wondering what the name for a section of the area between two concentric circles is called? It's essentially an isosceles trapezoid with the "parallel" sides now curved. I have Googled different iterations of "rounded trapezoid" and "2D toroidal section" etc., but have not found a term that I feel suits this shape.

I appreciate everyone's help.

• I don't think it has a known name. If you need one for something you are writing, make one up and tell your reader. "Angular section of an annulus" might do. – Ethan Bolker Dec 6 at 15:08
• It isn't a complete annulus, but part of one? – DanielOnMSE Dec 6 at 15:08
• annulus sector? This is how the wiki entry of annulus call it. – achille hui Dec 6 at 15:09
• Yes, I'm writing an academic journal paper and some of these terms are out of my wheelhouse. I appreciate the recommendation of defining my term for the reader. I just want to make sure I'm not making up a name for it if a name already exists. Imagine dancing around the word "triangle", haha. – kreeser1 Dec 6 at 15:12

In some contexts it's also called a "Polar Rectangle" since it is the region $$(r_0 \leq r \leq r_1) \times (\theta_0 \leq \theta \leq \theta_1)$$. That is, it's the product of two polar intervals.