In art and symbolism, a crescent (pronunciation: /ˈkrɛsənt/) is generally the shape produced when a circular disk has a segment of another circle removed from its edge, so that what remains is a shape enclosed by two circular arcs of different diameters which intersect at two points (usually in such a manner that the enclosed shape does not include the center of the original circle).

In astronomy, a crescent is the shape of the lit side of a spherical body (most notably the Moon) that appears to be less than half illuminated by the Sun as seen by the viewer. Mathematically, assuming the terminator lies on a great circle, such a crescent will actually be the figure bounded by a half-ellipse and a half-circle, with the major axis of the ellipse coinciding with a diameter of the semicircle. The direction in which the "horns" (the points at the intersection of the two arcs) face indicates whether a crescent is waxing (also young, or increasing) or waning (also old, or decreasing). Eastward pointing horns (pointing to the left, as seen from the Northern hemisphere) indicate a waxing crescent, whereas westward pointing horns (pointing to the right, as seen from the Northern hemisphere) indicate a waning crescent. Note that the directions the horns point relative to the observer are reversed in the Southern hemisphere.