a period from one new moon until the next.
a synodic month of approximately 29.53 days, measured from a lunar phase until the return of that same phase.
a sidereal month of approximately 27.32 days, the length of time taken by the moon in its orbit about the Earth to return to the same point as viewed against the background of stars.
A crewed artificial satellite designed for long-term habitation, research, etc.