👉 In mathematics, a semi-annulus is a type of annulus that has its outer boundary as an ellipse and its inner boundary as a circle. Semi-annuli are named after the two points at which they meet; one point is called the semi-axis, and the other is called the major axis. For example, imagine a semi-ellipse where the semi-axis is 2 units long (the longer line) and the minor axis is 3 units long (the shorter line). The
