Saline: Relating to salt. As an adjective, "saline" means "salty, containing salt." As a noun "saline" is a salt solution, often adjusted to the normal salinity of the human body.
Salt, in medicine, is referring to sodium chloride. Sodium chloride is common table salt and the salt concentrated in the earth and in sea water.
Certain concentrations of both sodium and chloride in the blood are essential for normal body functions. Saline solutions are commonly used in medicine as fluid replacements to treat or prevent dehydration.