Gayatri is said to be the oldest and greater of the Vedic mantras - Maha meaning great. It is a request to the Divine to remove obstacles of our mind, to show us the truth and to guide us on a higher path. It talks about connecting to the light of true and right knowledge. Through repetition, this mantra is said to project you and allow you to shine from the inside out.
There are many versions of the great mantra, we particularly love this one by Deva Premal.