The moon is waning when it is getting smaller
Waning.
Then the Moon is "waning".
waning
Waning.
When the moon appears to be shrinking, it is said to be waning. This phase occurs as the amount of illuminated surface visible from Earth is decreasing. It gradually transitions from a full moon to a new moon.
A "shrinking moon" refers to the phenomenon where the moon appears to be decreasing in size, usually during its waning phase. This is a natural occurrence as the illuminated portion of the moon visible from Earth decreases over the course of the lunar cycle.
Waning.
When the moon grows smaller, it is said to be waning. This is the period between the full moon and the new moon, when the visible portion of the moon decreases.
It is said to be waning, and waxing when the moon's light is increasing.
Waning gibbous, Third Quarter and Waning Crescent are the 'waning' moon phases.
The Moon appears to be waxing when it is transitioning from a new moon to a full moon, and waning when transitioning from a full moon to a new moon. Without specific information on the current lunar phase, it's not possible to determine if the Moon is waxing or waning at this moment.
A moon that gets smaller after the full moon is called a waning moon. It goes through phases from full moon to new moon.