Mantra meditation uses a word, phrase, or sound repeated silently or aloud as the object of focused attention. The repetition of the mantra gives the mind a simple, rhythmic anchor that helps prevent it from following distracting thoughts. Mantras appear across virtually every spiritual tradition — Om in Hinduism and Buddhism, So Hum (I am that), and various Sanskrit, Hebrew, Arabic, and Christian contemplative phrases. The mantra functions not as a prayer or affirmation but as a vehicle for stillness — its meaning is secondary to its ability to focus and settle the mind.

Reference:

Wikipedia: Mantra

https://en.wikipedia.org/wiki/Mantra