Answer may be:

“Om” 

Om is a sacred syllable of the Hindu religion and other religions mainly of India. Sages, monks, and yogis chant this during meditation. It is considered as greatest of all the mantras of all time. It is composed of three sounds a-u-m( a and u vowels coalesce to become o). It is considered the sacred sound of the universe. The symbol of “om” is usually written before any auspicious event in Hindu homes. It can also be written at the entrance of the house or as a rangoli or decoration to bring positive vibes.

It ( "Om" ) represents several triads like:

•  Earth, atmosphere and heaven.
• Thought, speech, and action.
• Goodness, passion, and darkness.
• Rigveda Yajurveda and Samaveda.
• It is the essence of entire universe.

It is chanted during Hindu prayers and also in Buddhist and Jain rituals. Chanting Om helps in releasing stress and brings positive energy. It also helps in controlling anger and clear our thoughts. While chanting Om vibration felt in our vocal cords helps clear sinuses. It also helps in bringing down blood pressure and improves the detoxification process of our body.