http://www.swamij.com Meditation on Soham mantra is a central mantra practice of Yoga Meditation. Soham is a universal mantra as it relates to the breath, and everybody breaths. SoHum is a Sanskrit word that means "I am that," or "I am that I am."

See also the video on Soham and Trataka (gazing).
http://www.youtube.com/watch?v=VBASQ314m7c