According to Wikipedia, a mantra is a sound, syllable, word, or group of words that is considered capable of creating a transformation. Om Mani Padme Hum is a chant often spoken out loud or silently by Tibetan monks in order to transform them into a state of peaceful bliss. By saying this mantra, Tibetan monks invoke the blessings of Chenrezig, the Bodhisattva of Compassion, whom is a central figure in Tibetan Buddhism. Not only is this mantra used by Tibetan monks, but by Buddhists throughout Asia including Japanese, Korean, Thai, Vietnamese and Malaysian.
Chenrezig is said to have wanted to help all of humanity to escape the realm of suffering, but upon his attempt to do so, he realized that there were too many people suffering for him to help. In frustration from his hard work and lack of success, his head split into a thousand pieces. Amitbha Buddha put the pieces of Chenrezig’s head back together and gave him many heads and arms so that he better try to help all of the people suffering in the world.
Om Mani Padme Hum literally translates into “Behold, the jewel is in the lotus” and each syllable has a specific meaning when spoken or thought. Om means behold, Mani means Jewell, Padme means lotus flower and Hum means “to be in”. It is a six syllable Sanskrit mantra and can often be found carved into rocks, painted on walls, or on Tibetan prayer wheels. Tibetan prayer wheels are actually known as Mani wheels, which is a part of the mantra itself (Om Ma Ni Pad Me Hum). When the mantra is painted on a wall each syllable is painted a specific color. Om is painted white, Ma is painted green, Ni is painted yellow, Pad is painted sky blue, Me is painted red, and Hum is painted black.
Om = purifies bliss and pride
Ma =purifies a lust for entertainment and jealousy
Ni=purifies passion and desire
Pad =purifies stupidity or prejudice
Me =purifies poverty or possessiveness
Hum= purifies aggression or hatred
It is very good to recite the mantra Om Mani Padme Hum, but while you are doing it, you should be thinking of its meaning, for the meaning of the six syllables is great and vast. – Tenzin Gyatso, The 14th Dali Lama
Check out this link to listen to the mantra spoken by Tibetan monks.