Om (Oum) is the imperishable syllable (Akshara). It symbolizes the universe. The whole Mandukya Upanishad is devoted to the delineation of Om. I will quote only English translation of the first verse from Mandukya Upanishad for simplicity.

'Om, this syllable is all their is at present, all there was in the past, all there will be in the future and whatever else beyond all these there is also Om'. The Gayatri Mantra is the mantra of the highest order which incorporates all the ideas and inner meaning of the Om-symbolism. It is a prayer to the supreme Absolute Reality of the enlightenment of the intelligence (Dhi) of all human beings to enable them to realize the supreme truth. It is also know as the Savitri Mantra, since it is addressed to the divine being in the Sun (Savita), who is considered as the visible symbolic representation of the supreme divinity since He destroys darkness and promotes life. The implicit meaning is that He, the Sun is identified with the inner self of man (Isha Upanishad, 15-16).

Savitri signifies that which is related to Savitr (Savita), which means the source or the originator of the universe (Brahman) as well as the Sun. Savitri Mantra occurs in the Vedas (Rik Veda, III.62.10) and is considered to be the very essence of Gayatri mantra, or even their Mother (Gayatri, Veda mata). Later on Gayatri was associated with Om, which is also considered as the source of all Vedas. Through this interconnection, Gayatri was treated as the elaboration of Om.

The utterances of the divine creator representing the tree cosmic planes, Bhur-Bhuvah-Suvah (Brihadaranyaka Upanishad, V.14: 1-8; Chhandogya Upanishad II: 2.3.2-3:III.12) embodied in the Gayatri Mantra run as follows 

'Om, We mediate (Dhimahi) on the spiritual effulgence (Bhargas) of that adorable supreme divine reality (Varenyam Devasya), the source of the three phenomenal world planes - the gross or physical (Bhuh), the subtle or physical (Bhuvah), and the potential or casual (Suvah), both macrocosmically (externally) and microcosmically (internally). May that supreme divine being (Tat) stimulate (prachodayaat) our (Nah) intelligence (Dhiyah) so that we may realize the ultimate truth'.

The Gayatri Mantra is the most universal , non-personal prayer, which can be used by any person irrespective or race, religion, gender or color. Let all human beings, in tranquility, mediate on the Gayatri Mantra as beginning, ending and breathing in the Brahman, and realize the Absolute Reality and attain moksha, liberation.