Saline is an adjective that means "salty." While "salty" is a perfectly good word to use when describing French fries or tears, saline tends to be a word you might hear in a more official setting, like in a hospital or in a geology class.
If you watch a lot of hospital dramas on TV, you have definitely heard the exclamation, “Nurse, the patient needs an IV saline solution, stat!” because sick people in hospitals tend to get saline solutions to keep them hydrated. Saline mostly has a scientific meaning; it is not usually used to mean salty tasting. If you want to get really scientific, salt is actually called sodium chloride, but "sodium chloride pretzels" would probably not fly off the grocery store shelves.