A mantra is a word or phrase that you repeat to yourself (silently or out loud) that helps you to remain focused during your meditation.

The sound of the mantra itself has a meaning due to the vibrational energy that comes from repeating the sound. Chanting a mantra for a certain amount of time you’ll find yourself completely immersed in it.  

There are Ohm or Aum mantras, which point directly to the divine/eternal within. The 30 minute So Hum meditation stands for ‘I am That’ which points to the same as Ohm. The 15 and 20 minute chakra seed mantras are supposed to cleanse & energize the energy points in the body, also ending with Ohm and Aum.