The twelve moons of Munnopor is a spell dependent on the deity called Munnopor. This spell is used to cancel an enemies spell.
When Doctor Strange went into the Dark Dimension to save Spider-Man the two of them headed toward a portal that lead back to Earth. However, Dormammu was able to seal the portal. Doctor Strange then invoked the twelve moons of Munnopor which canceled Dormammu's spell and removed the barricade and allowed them to go back to Earth.