Meaning of mantra in Hindu scriptures mean the 'sacred utterance' but is explained in a different way.
In Agamarahasya (XXIII. 2.), the word mantra is analysed in terms of manana (contemplation) and trana (protection).
Manana is explained as the knowledge of the world.
Trana means freedom from the bondage caused by the world of experience.
A similar definition of mantra, namely, “that which helps to free the individual from the bondage of samsara is found also in the Vatula Suddha Tantra (V.7.)
Such power of the mantra issues from the fact of being the same thing as Sabda Brahma.
Every mantra used for japa is supposed to have a presiding deity, called the adhisthatri devata of the mantra.
For instance, the devata of the famous Gayatri Mantra is the sun god – Surya.