The Triple Goddess symbolism is associated with neopaganism, particularly the Wicca tradition. It refers to a goddess who represents the three different stages of a woman's life: Maiden, Mother, and Crone (or Witch). These stages are correspondingly associated with the different phases of the lunar cycle: waxing moon, full moon, and waning moon.
Virgo (waxing moon) represents youth, innocence, new beginnings, and growth.
The Mother (full moon) represents maturity, fertility, motherhood, and fulfillment.
The Old Woman/Witch (waning moon) represents wisdom, life experience, and the end or death.
Wicca and other neopagan movements see the Three Moon Goddess as an important figure who connects these different stages of life and lunar cycles together.
"The Goddess of the Three Moons" is not a historical designation, but a modern creation, born as part of the neopagan movement of the mid-20th century. The term is therefore a proper name to describe this neopagan concept, but it does not originate from ancient religious or mythological traditions.