The Hare Krishna mantra, also referred to reverentially as the Maha Mantra “Great Mantra”. This Mantra is composed of three Sanskrit names of the Supreme Being; “Hare,” “Krishna,” and “Rama.

हरे कृष्ण हरे कृष्ण , कृष्ण कृष्ण हरे हरे |
hare kṛiṣhṇa hare kṛiṣhṇa kṛiṣhṇa kṛiṣhṇa hare hare

हरे राम हरे राम , राम राम हरे हरे ||
hare rāma hare rāma rāma rāma hare hare

The three words— Hare, Krishna, and Rama—are the seed sounds of the maha-mantra, Hare refers to the energy of that One Infinite Source of all of us. The energy thats present all around us.
Rama and Krishna refer to incarnations of Lord Vishnu.
When Chanting this Mantra, we are calling for that universal energy.