That which through manana (contemplation) helps to attain trayate (liberation) is mantra.
Mantras are not mere incantations. They are sacred syllables. They are invocations to particular deities, which recited repeatedly in meditation turns into an illuminating experience for the sadhaka. In other words, the sakti (power) which leads to enlightenment is latent in mantras and reveals itself to him as conscious energy.
Mantras occupy a significant role in the tantras. Tantrik sadhakas believe in the eternity of the mantras which are collectively termed the Sabda Brahman. Sabda means sound. The tantrik school teaches that sadhakas attain salvation only through the incessant japa (repetition) of mantras.