Here is an extract about the Om Ah Hum mantra. The full piece of writing can be found here:
“Om ah Hum” is a well-known Buddhist mantra, but what does it mean? It is a mantra that functions on many levels. The following is a basic explanation.
The Tibetan Buddhist Chant of Om ah Hum also contains these sounds. The Om ah Hum, the Mantra of Blessing frequently precedes the recitation of other mantras.
The sounds Om, Ah and Hum are individual Sanskrit seed syllables. The first thing we notice is that consists of three words, what immediately implies the symbolism of any trinity. In Buddhism the most common found trinity is that of Body (kaya), Sound or Speech (vak) and Spirit or Mind (citta). The perfect state of being of each of these three bodies is symbolized by the three words of Om a Hum. The Body is not only the physical body of man but also the entire material dimension of the individual. The Sound is the life energy of the Body, known as prana. The Spirit is the reason and that what is behind the reason.