A crescent shape (ˈkrɛsənt, UKalsoˈkrɛzənt) is a symbol or emblem used to represent the lunar phase in the first quarter (the "sickle moon"), or by extension a symbol representing the Moon itself.
In Hinduism, Shiva is often shown wearing a crescent moon on his head symbolising that he is the master of time and is himself timeless.
It is used as the astrological symbol for the Moon, and hence as the alchemical symbol for silver. It was also the emblem of Diana/Artemis, and hence represented virginity. In veneration of Mary in the Catholic Church, it is associated with Mary, mother of Jesus.
From its use as roof finial in Ottoman mosques, it has also become associated with Islam, and the crescent was introduced as chaplain badge for Muslim United States military chaplains in 1993.
The crescent symbol is primarily used to represent the Moon, not necessarily in a particular lunar phase.
When used to represent a waxing or waning lunar phase, "crescent" or "increscent" refers to the waxing first quarter, while the symbol representing the waning final quarter is called "decrescent".
The crescent symbol was long used as a symbol of the Moon in astrology, and by extension of Silver (as the corresponding metal) in alchemy. The astrological use of the symbol is attested in early Greek papyri containing horoscopes.
In the 2nd-century Bianchini's planisphere, the personification of the Moon is shown with a crescent attached to her headdress.
Its ancient association with Ishtar/Astarte and Diana is preserved in the Moon (as symbolised by a crescent) representing the female principle (as juxtaposed with the Sun representing the male principle), and (Artemis-Diana being a virgin goddess) especially virginity and female chastity.
In Christian symbolism, the crescent entered Marian iconography, by the association of Mary with the Woman of the Apocalypse (described with "the moon under her feet, and on her head a crown of twelve stars" in Revelation)
The most well known representation of Mary as the Woman of the Apocalypse is the Virgin of Guadalupe.