A nonconvex plane figure bounded by the arcs of two circles with the same endpoints.
- A lune has a crescent shape.
- In the example below, each of the two lunes is constructed from the arcs of circles of three radii, that is, AB, AC and BC. The sum of the areas of the two lunes is equal to the area of triangle ABC.
The lunes illustrated in the example are called Lunes of Hippocrates (Hippocrates of Chios, 5th century BC).