What term can also be used to describe sub-atmospheric pressure?

The term that can also be used to describe sub-atmospheric pressure is "vacuum." In scientific and engineering contexts, a vacuum refers to a space where the pressure is lower than that of the surrounding atmosphere, which is effectively sub-atmospheric pressure. This concept is important in various applications, including plumbing and backflow prevention, where maintaining specific pressure levels is essential for preventing contamination and ensuring system integrity.

While "negative pressure" might seem like a suitable alternative, it generally describes pressure lower than a reference point and can vary widely, not specifically indicating a vacuum state. "Low pressure" is a relative term that doesn’t inherently mean a vacuum, as low pressure can still be above atmospheric levels. "Atmospheric pressure" refers to the pressure exerted by the weight of the atmosphere and is not applicable when discussing conditions that are below this pressure level. Thus, vacuum is the most precise term for describing sub-atmospheric pressure in this context.