Gayatri (pronounced as Gaayatree) is a Sanskrit word, made up of two syllables - "Gaa" and "Yatree". "Gaa" means to sing and "Yatree" means protection. So Gayatri means those who "worship her, or sing her praise, get protected".
Gayatri is not a new or independent goddess. She is the supreme power (Shakti) of Lord Brahmaa, Vishnu, Shiv, Raam and Krishn. Lord Raam who came on this Earth in Tretaa Yug, took the Deekshaa of Gayatri Mantra from Muni Vishwaamitra Jee. Lord Krishn, who came on this Earth in Dwaapar Yug, took the Deekshaa of Gayatri Mantra with His friend Sudaamaa from their Guru Saandeepan Muni. Even the Godhead Shree Krishn says in the Holy Geetaa - "Among all the Mantra I am the Gayatri Mantra".
Otherwise Gayatri is a type of Sanskrit poetry which has only 24 syllables - 8 syllables each in three lines. This Gayatri Mantra also has 24 syllables, that is why it is called Gayatri Mantra.
Gaayatree as Devee
Gaayatree is a Devee also who removes ignorance and lets her Bhakt see the spiritual sunlight. She is depicted with five faces with different colors, carrying different things, with ten graceful eyes, sitting on a red lotus. Each of her five faces signifies a specific meaning such as ---
(1) Pearl Color - Pearls are collected from the sea from shells. These shells come to the shore of the sea with their eyes and mouth open. When it rains, the rain drops fall into their mouth and if at the time the rain drops fall into their mouth, the Swaati Nakshatra (star) is in the sky, they absorb its radiation into them, then the rain drops are converted into original pearls (as distinct from cultured Pearls). These original pearls are Divine in nature. Thus the first face of Gaayatree is of Pearl color, giving out the luster of Pearls representing brilliance.
(2) Coral Color - (bright red) Coral is one of the nine gems. The second face develops the principle of Nishchal Tattwa in the aspirants mind - still mind.
(3) Gold Color - Very bright both in color and quality. Mere seeing the gold and exposing ourselves into its luster promote good quality and external charm in the aspirant.
(4) Blue color - represents the Sky. Sea is also blue in color. Vishnu is also blue in color - Vishnu Tattwa. This face fosters the aspirant with all wealth and also Divine Grace from Naaraayan.
(5) White face -This face represents purity. It develops purity in the mind of the aspirant and also grants divine grace from Saraswatee - the goddess for wisdom.
Gayatri is the Aadi Shakti, initial power or prime power, which gives the movement, force or inspiration to both living and nonliving things. Gayatri Poojaa is done by chanting Gayatri Mantra, or by worshipping the Gayatri Yantra, or by conducting the Gayatri Anushthaan.
Picture of Gayatri Maa
This picture of Gayatri Maa is made on the basis of a Shlok from "Sharada Tilakam". Based on this Shlok, many pictures of Gayatri Maa were drawn and are available, but one picture which is very close to the description given in that Shlok is given here along with Shlok and its meaning. This Shlok is also the Dhyaan Shlok for invoking Gayatri before starting her Jap during Sandhyaa Vandan -
Muktaa Vidrum Hem Neel Deval Chhaayai Mukhais Tri-kshanai
Yuktaam Indu Kalaa Nibaddh Mukutaam Tatwaarth Varnaatmikam
Gayatri Varad Abhayaangush Kasaas Subram Kapaalam Gadaam
Shankham Chakram Atharavindaa Yugalam Hastair Vaahanteem Bhaje
I sing in praise of Gayatri, who has five faces of the colors of pearl, coral, gold, blue, and white, who has three eyes
Who has the crescent moon in the crown, who is of the form of the (24) letters, describing the Tattwa
Who shows Varad and Abhaya Mudraa in two hands and holds the Ankush, whip, the white skull, the Gadaa
The conch, the Chakra and the lotus (in the other eight hands)
This picture shows --
--The five faces of Gayatri - five parts of Gayatri Mantra
--The crescent Moon on the crown, the three eyes and the skull are symbolic of Shiv, the Destroyer
--The conch, Chakra, Gadaa, lotus, the Abhaya Mudraa denote Vishnu, the Protector
--The lotus seat is symbolic of Brahmaa, the Creator
--The Ankush and whip symbolize Kaalee, the Shakti
Thus, in short, (see also Why Gayatri Mantra is a Mahaa Mantra)
--Gayatri is symbolized as Sarv Devtaa Swaroop - Brahmaa, Vishnu and Shiv.
--Gayatri denotes the three Ved that is why she is called Ved Maataa.
--Gayatri is the extension of the primordial sound Aum.
--Gayatri denotes subjects as he plural, that is why even if an individual chants it, the benefit goes to humanity.
--Gayatri has 24 letters which denote 24 principles.
--This picture is for a Grihasth to meditate upon, a Brahmchaaree should always meditate upon her as a light.