As you cool air, it cannot hold the same amount of moisture. At some point, that air will become saturated and moisture will begin to condense out of the air onto any adjacent surface.
When it condenses, at that point it is called “Dew Point Temperature”. For example, take a cold can of pop and place it outside on a 90 degree day. What happens? It begins to sweat, or in our terms it has reached its dew point temperature. The design objective for pool enclosures is to ensure that no surface within the pool enclosure or within the structural members reaches dew point and cause moisture to condense.