Which of the following defines the low pressure zone in fluid dynamics?

The correct choice defines a low pressure zone in fluid dynamics as an area where the air density is lower due to rapid movement. In fluid dynamics, low pressure zones often occur as a result of high-velocity flow. According to Bernoulli's principle, when the speed of a fluid increases, its pressure decreases. Therefore, in regions where air is moving rapidly, such as in the wake of an object or within certain types of airflow patterns, the air density diminishes, leading to lower pressure.

This concept is critical in various applications, including aircraft wing design, where the shape of the wings creates different airflow velocities above and below them, resulting in lift. Understanding the characteristics of low pressure zones is essential for analyzing how fluids behave in different contexts. The other options do not correctly describe a low pressure zone in terms of velocity and its impact on air density.