Salinity refers to the amount of salt contained in a given sample of water. When salt water from the ocean mixes with fresh water from the land it produces brackish water in the Chesapeake. This range of salt levels will impact which organisms can live there.
Here is a series of articles about Salinity in estuaries from Freshwater Inflow.
NASA provides a map of salinity levels in all of the world’s waterways.
Here is a video that shows how the salinity of the Bay changes over the course of a year.