The Great Mother

She is the Spirit of Earth and Sea and Sky, the Mother of All. The World is Her Body. But She is not merely a birth mother, for She is also a matriarch, an administrator, an executive. Sometimes considered the consort of the Horned Harvest Lord, there is nothing androgynous about Her, as She embodies full, actively manifest Womanhood.

Mari (Basque)
Tiamat (Mesopotamian)
Diana (Roman)
Ashtart, Astarte, Ashtaroth, Ashtoreth
(the first is her actual Phoenician name, the second is the well-known Greek form, the last two are Hebrew perversions of the original Phoenician)
Yoni Gorri, the Red Mari (Gypsy)
Parvati, Devi (Hindu)

She is visualized as tall and naked, standing on the Sea. Her long black hair covers her like a veil. Her body is silver. She has 12 stars around her head, or in some descriptions, 6 and 7. Her breasts are full and heavy, and Her belly is rounded and swollen. She is ripe.

Her symbol is the Full Moon.

Great Mother Visualization

Starhawk has a useful meditation on Her in The Spiral Dance, in Chapter 5: The Goddess, Exercise 40: Full Moon Meditation.

Visualize a round full moon. She is the Mother, the power of fruition. She nourishes what the New Moon has begun. See her open arms, her full breasts, her womb burgeoning with life.
Feel your own power to nurture, to give, the make manifest what is possible. She is the sexual woman; her pleasure in union is the moving force that sustains all life. Feel the power in your own pleasure, in orgasm. Her color is the red of blood, which is life. Call her name "Mari!" and feel your own ability to love.