OM is defined as “yes, verily, so be it.” OM is the hum of the universe, the primordial song of the universe saying YES to its own expansion.
OM is composed of the 3 sounds A U and M.
If you listen to people, A U and M, and sometimes OH are the kinds of sounds people make when they are saying yes to something. Ah, yes! Oh, yes. Mmm yeah. Yes, that is great.
People make these sounds when saying yes to satisfied desire.
OM is “Bring it ON!” Let the games begin. Let the play unfold.
Further on in the definition of OM it says, “OM is usually called pranava.”
As Chris Chapple writes in Yoga and the Luminous, 1.27
pranavah (m. nom. sg.) the sacred syllable "om' ; from pra (before, forward) + nava, from nu (sound, shout, exult) Its expression is pranava (om). “Exult” is generally defined as “to rejoice greatly. Be jubilant or triumphant. To leap upward, especially for joy.” - Christopher Chapple. Yoga and the Luminous: Patanjali's Spiritual Path to Freedom (p. 152). Kindle Edition.
OM and pranava are nicknames of each other and pranava means a “shout of exuberance.” Latin exsultāre : ex-, ex- + saltāre, to dance, frequentative of salīre, to leap. Pranava suggests leaping forward. In meditation, we are attuning our nerves and senses, recharging, and getting ready to leap up and dance.
Mantra yoga is a way of bathing in your primordial yes to life and restoring it if you have lost it. When we go deep with a mantra, and allow for the whole cycle of resting and restoring, we can recover our exuberance.