Gayatri is recited by a spiritual aspirant to remember the higher purpose of life, it can also be an invocation or prayer to God in order to lift our consciousness upwards. It is usually recited by the people who consider ‘knowing the ultimate truth’ as the primary purpose of their life.
Om, Bhur, Bhuvah, Svah [Ultimate reality, in which physical, astral and causal worlds exist]Om: The sacred word, word of creation, first word, word of God; (Equivalent of Holy Ghost in trinity) usually used at the beginning of a hymn; Bhur: The physical plane of existence (which is of the nature of 5 elements) Bhuvah: The astral plane of existence (which is of the nature of subtle elements)Svah: The causal plane or celestial plane (plane where the existence is as subtle as ideas or notions, from which creation happens).  
Tát savitúr váreṇyaṃ [That is the Supreme reality from which creation happens, and it is the foremost]Tat: That, God, (Equivalent of Son, in the Christian Trinity of Father, Son and Holy Ghost) Savitúr : Source of all, creation, supreme reality, Divine illumination (of goddess Savitri or Shakti) Váreṇyaṃ: the foremost, fit to be worshiped, deserving oblations 
Bhárgo devásya dhīmahi [O Divine effulgence we meditate upon you]Bhárgo: Great spiritual effulgence, Radiant one, one who illumines all Devásya: Godly, divine reality, of divinity, Virtuous and joyous Dhīmahi: We meditate on you; Dhee=intellect; Thus Dhimahi means we focus our intellect on you
Dhíyo yó naḥ pracodáyāt [propel our knowledge of the supreme reality]Dhíyo: Intellect, intelligence, reasoning and discriminating faculty which is a tool for attaining higher wisdomYo: Who, One is who being prayed, You (Supreme One) Nah: Our (intellect) pracodáyāt: Stimulate, Propel towards the higher reality