Mantras are words or phrases that are chanted out loud or internally as a meditation or prayer. Often these mantras are associated with particular religious figures or states of being, whose qualities can be cultivated by the repetition of the relevant mantra.
Certain cultures believe in the sacred power of words, and believe that saying certain words or names can control the external world, or control unseen forces that may affect them.
As an example, one could say that the Catholic rosary (used regularly) is also a 'mantra'.
Mantras can also take the form of positive affirmations - for example:
I choose love, joy and freedom, open my heart and allow wonderful things to flow into my life.
Many people claim that positive affirmations (when used regularly) help re-program the brain and assist you to think differently about things.