Mahavidya means great knowledge and refers to a female deity; there are ten such deities. Knowledge is transcendental and all that is known, unknown and yet to be known. What Mantra is to a male god is Vidya to a goddess. Mantra or Vidya consists of one or more syllables with or without meaning, words, or phrases representing (being) the sound-body of a deity; there are ten great Mantras or Vidyas. If your name is Joan Smith, the vocalized sound of your name or JS is your sound-body; you and the sound-body are one; that is the power of sound or sabda. Pronunciation of Mantra is important. What if somebody mispronounces your name as John Smythe? Would you answer the caller? The vibrations of deity-specific Mantra, when chanted according to the rules of Tantra, bounce off Yantra , go to the specific deity, gather power, blessings and boons from the deity and come back to the Sadhaka (chanter of Mantra), suffuse him with divinity and confer on him supernatural powers. Yantra = instrument, engine, apparatus, amulet with mystical diagram endowed with protective occult powers (Raksha Yantra). Yantra is a plate or paper on which geometric figures are drawn which concentrate the power of goddess. Yantra is the diagrammatic representation of a deity. Yantra can also be a three dimensional piece. Mantra (or Vidya), Tantra, and Yantra are complementary and necessary for supplicating the deity according to the rules of Tantra, bouncing the petition off Yantra, sending it on its way to the deity, and receiving the rewards from the deity.