A mantra is a sequence of words or syllables that are chanted, usually repetitively, as part of Buddhist practice. An example of a mantra is om mani padme hum, which is associated with Tibetan Buddhism.
The function of a mantra is understood differently by the several schools of Buddhism, but at its most basic level, the chanting of a mantra is thought to evoke enlightenment. Sometimes mantras are used as a form of meditation.
Different mantras evokes different kinds of blessings to assist us in our worldly or spiritual pursuits, but it must always comes with pure motivation.