HU is a sound, like OM, which is a representation of the energy stream that flows through all of life. Using it can put you in touch with the Flow very quickly. It is an ancient mantra, and is found in many mystic traditions throughout the world. Some people use it as a meditation aid: to still the mind, to feel life's Oneness or even for help in making a decision.

It is pronounced either hoo or hue (hue being the more preferred version that I'm aware of). It can be sung at any time, in any situation. It can be sung at any tone, with any variation, in breaths long or short. The spiritual path of Eckankar ("co-worker with God") refers to it as "A Love Song to God." There is evidence that this may have been the first word humans used to address the divine.

You can even sing it silently. There are many interesting tales about things that happen with people when they're singing HU, for themselves or for others. It usually serves to calm someone's distress or to reorient a situation. Occasionally it creates a connection to some interesting visual/sound/meditative phenomena.

  Click on this link to an audio clip from the website for Eckankar. It includes a recording of over 1000 people singing HU.