To understand the meaning of Avalokiteshvara's six-syllable Mantra a thorough and detailed interpretation should be sought from commentaries and the oral explanations of noble scholars, who have extensive understanding of the meaning of tantra. Here, I will just give the gist of it.

The syllables of the Mantra are, Om-ma-ni-pad-me-hum. The first syllable OM represents the Form Body of a Buddha, and the last syllable HUM represents his Truth Body. MANI means wishfulilling gem. symbolizing the pure Wisdom that has realized emptiness. The vowel E ending the word PADME has been described as a call to someone. It is essentially a short symbolic supplication to Avalokiteshvara saying,

'O, Supreme Avalokiteshvara, you have attained the two Bodies of a Buddha through the dual path of wisdom and method, indicated by the jewel and lotus you hold, please lead all sentient beings to attain the two Bodies of Buddha as you have done!