What is the definition of waxing moon and waning moon?

What we see: Gradual increase of sunlit surface of the Moon, from New Moon (zero sunlit surface of Moon/) to Full Moon (whole disk sunlit) is called waxing. The opposite is waning.

Moon shows nearly the same face in its orbit around yhe Earth. During this period of nearly 29.53 days, it turns about its own axis in facing . So, in our view, the sunlit portion of its surface is waxing for half this period and waning for the other hall.