What is the primary astronomical requirement for a new or full moon to be considered a supermoon?

Answer

It must occur near the Moon's closest approach to Earth in its orbit (perigee)

A supermoon describes a new or full moon that happens when the Moon is near perigee, which is its closest point to Earth during that specific orbit.

What is the primary astronomical requirement for a new or full moon to be considered a supermoon?
astronomysupermooneffect