Final answer:
The curved boundary in a Psychrometric chart defines the saturation point, where air contains the maximum water vapor it can hold at a given temperature, with any further moisture leading to condensation.
Step-by-step explanation:
In a Psychrometric chart, the curved boundary represents the point of saturation. This boundary, also known as the saturation curve, delineates the conditions under which the air is fully saturated with water vapor. When air at a certain temperature contains the maximum amount of water vapor it can hold, it reaches saturation. Beyond this point, any additional moisture will result in condensation or dew. The saturation curve is a fundamental concept in understanding psychrometric processes and is crucial for various applications, such as HVAC design and meteorology.