What is hydrostatic pressure?

Hydrostatic pressure refers to the pressure exerted by a fluid at rest due to the force of gravity acting on it. This pressure increases with depth in the fluid, as the weight of the fluid above exerting force on a given area contributes to the overall pressure. In the context of option B, it describes how a volume of fluid, such as water in a tank or ocean, exerts pressure against the walls or structures supporting it. This concept is critical in various applications, including engineering, architecture, and fluid dynamics, where understanding how fluids interact with surfaces is essential.

The other options pertain to different types of pressures or concepts in fluid dynamics. Pressure exerted by a gas in a closed container relates to atmospheric pressure, while thermal expansion of fluids and pressure resulting from fluid motion are different phenomena that do not specifically describe the static pressure exerted by a fluid at rest.