x1 is the conceptualized/ideal/abstract shape of a crescent/concave 'horned' (then convex rounded) form/geometric partially-concave lune formed by/manifested from the intersection x2 (parameters) of two-dimensional circular disks immersed (embedded) in geometry/defined by metric x3
x2 can explicate any relevant characteristics and parameters that describe the intersection of the two-dimensional circular disks, such as: the radii of the circular disks, the relative location of their centers/perimeters, the direction in which the 'horns' of the crescent are facing. The shape is itself two-dimensional, but may be immersed/embedded in a greater-dimensional space or in a non-Euclidean metric (such as Manhattan space or spherical geometry); due to some ambiguity in naming of the shape in spherical geometry (confer: lens/tairbagycukykruca), other words are probably preferred for the area bounded by intersecting great circles in such a context (see: spherical great digon, Zweieck). The lune in this sense is a "filled area": it is a disk less an intersection (with another disk). See also: cuktai, tairjirnycukykruca, tairbagycukykruca, tarmi, simlu, mluni, lunra, plini