From a recent talk by Ganga.  

OM is a wonderful, effective, and beautiful way to bring the attention and energy of a group to one place—the same place. When you begin a class and say, “OK, we’re going to start, attention please!” Some are listening, some are not, and it’s hard to gather the attention. When you chant OM, everyone comes to right here and now. It brings everyone right to the present moment. I think that is as good a definition and meaning of OM as anything.

People will ask, “What does OM mean?” You really cannot actually or strictly translate it. It has no definition, it means nothing, and it can also mean everything. The sound is a symbolic sound or attunement. OM points toward something and has import or direction. It points toward everything and nothing, toward what is and what isn’t, and toward the inner, and the outer. Ancient Yoga philosophy had some idea that everything in the universe is energy and vibration. They may not have necessarily understood this scientifically since there were many things they didn’t know or understand, but their idea about the universe turned out to be more or less true—that the universe is made of energy and vibration. Chanting OM harmonizes you with that universal vibration.

OM is said to contain all sounds. The verbal sound starts gutturally with Ahhh, and becomes uuu as the mouth closes, and with the mouth completely closed, becomes mmmm vibrating the top of the head. It is actually not correct, though you will hear teachers say, that om should be broken into the separate vowels a, u, m. Some teachers say it should be chanted with aaa ooo and mmm as three separate syllables, but this isn’t accurate. The letter in Sanskrit is one symbol, one letter, and represents one sound. When that sound is made as one oooommmm you still have all three syllables and sounds contained therein. The aaa, the uuu and mmm are all there and contain more or less the range of verbal sounds. OM begins with a low tone, vibrates low, especially with a deeper voice, and as you close your mouth you feel the sound move up the spine to the top of the head carrying the vibration to the crown.

One way I often translate OM, is “what you feel and experience when you chant it.” There is resonance, there is harmony, and there is connection between everyone, and there is bringing everyone to the same point. That’s powerful, that’s beautiful; it’s simple. And it freaks some people out! Some people may think oming is weird, and I get that. And some also think it’s going to destroy their religion. I’ve taught in churches and some places where we weren’t allowed to chant OM. So I would say, “Well, it’s the same as amen”. They might reply, “Ok then let’s just chant amen instead of OM. Religion is most often programmed in with fear, but that’s another conversation…

OM means everything; it means the vibration of the universe; it means harmony; it means resonance, oneness, connection. OM is part of all that; it is all that. We could also add that you often hear OM
chanted three times. There is no rule. You may chant it once, three times, five times. It’s commonly done in threes, and there may be no provable reason, but there are some good theories, or perhaps truths. There are many threes in life. There are is the higher, the middle, and the lower. There are the body, mind and spirit. There are the past, present, and future. There are you, me, and we. These are some good reasons to chant in threes.

A continuous OM is also powerful and beautiful. The group begins together chanting OM, then lets it go on for however long the group dynamic makes it last. It may go on for two minutes or five minutes or however long it continues naturally. There is the starting point and then just letting the vibration and sound go. Each person comes in and out at their own pace, harmonizing, and tuning to the quality and energy of the group OM and letting that group OM feeling express itself and relate through your own individual contribution which becomes the fabric of the group chant–that is also a profound lesson in life. That is what OM points toward—the vibration, sound and silence of the universe, the one and the many, the inner and the outer, everything and nothing.