What is the best word or term to describe a shape which is a subset of an annulus?

Question

The shape has two arcs with the same center, and two straight line segments which would be part of radii of the circles. So the shape can be described by 'inner radius', 'outer radius', 'begin angle', 'end angle'.

Answer 1

I found enough credible references on Google to justify calling it a "semi-annulus".

Or a "rainbow". ;c)