Definition - What does Maha Mantra mean?
The Maha mantra is chanted for the benefits of the energies of the three Hindu deities referred to in the mantra. The name comes from the Sanskrit, maha, meaning “great”; man, meaning “to think”; and tra, meaning an "instrument" or "tool." A mantra, therefore, is an “instrument of thought.”
In yoga, chanting a mantra focuses concentration on a single thought or stills the mind in meditation.
The Maha mantra is also known in English as the Great mantra or the Hare Krishna mantra.
Yogapedia explains Maha Mantra
The vibration of the mantra sounds is thought to activate spiritual energy. Specifically, the Maha mantra is chanted for God-realization and to achieve a higher level of consciousness. The Maha mantra repeats just three words/names: Krishna, Rama and Hare, which is believed by some to be the energy of Hari (Vishnu) and to others, Hara (Shakti).
The full text of the mantra is:
Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare
Hare Rama, Hare Rama, Rama Rama, Hare Hare.
This mantra is recited in some songs popular in American and European culture, most notably former Beatle George Harrison's “My Sweet Lord.”