Which term defines the saltiness or dissolved salt content of a body of water?

Salinity is the term that specifically refers to the concentration of dissolved salts in a body of water. It is typically expressed in parts per thousand (ppt) and is a crucial factor in understanding various aquatic environments, including oceans, estuaries, and freshwater systems. High salinity is characteristic of seawater, while lower salinity levels are found in freshwater bodies like rivers and lakes.

Understanding salinity is essential for studying marine biology, as it influences the types of organisms that can thrive in a particular environment. It also affects water density, circulation patterns, and overall ecosystem health. The other terms listed do not pertain directly to the concentration of salts in water. For instance, acidity refers to the pH level of water, hydration pertains to water's ability to maintain moisture, and freshness typically describes water that does not contain significant dissolved salts.