Japa, in general, is devotional repetition, aloud or mentally, of sacred prayers, words, or names of God. Chanting of any word creates a certain vibration; practice of japa fills the mind with holy vibrations that neutralize vibrations of material consciousness. There are special incantations used in India, called mantras, which have great vibratory force. (The proper use of specific mantras that elevate the consciousness Godward—as meditation on Aum, for example—is a sacred part of the science of Kriya Yoga.) Repeating them aloud or mentally—with sincere feeling, intelligent understanding, and intense concentration and determination to persevere until divine contact is actually felt—produces distinct results; body and mind are charged with power as their vibratory rate is heightened.
See also: Chanting