Gayatri is the feminine form of gayatra, a Sanskrit word for a song or a hymn, having a Vedic meter of 3 padas or lines of 8 syllables. In particular it refers to the Gayatri mantra, and the Hindu goddess Gayatri as that mantra personified.
Gayatri is typically portrayed as seated on a red lotus, signifying wealth. She appears in either of these forms:

• Having five heads(Mukta, Vidruma, Hema, Neela, Dhavala) with the ten eyes looking in the eight directions plus the earth and sky, and ten arms holding all the weapons of Lord Shiva, Lord Vishnu & Lord Brahma.

• Accompanied by a white swan, holding a book to portray knowledge in one hand and a cure in the other, as the goddess of Education.

She is an aspect of Mata Saraswati, Mata Lakshmi and Mata Parvati, all three in one form, a form of Adi Shakti, possessing the Rajasi Guna and hence is the source of Brahma's power. Without her, Brahma remains dormant or unable to create. It's said that if we worship anyone, Gayathri Lakshmi Saraswati Durga or Radha devi it is equal to worshiping all the pancha matha.

Gayatri Chalisa with Audio and lyrics
Gayatri Aarti with Audio and lyrics
Gayatri Mantra with Audio and lyrics