The chemical formulas H2O and NaCl stand for water and common salt; when mixed, they produce a saltwater solution. Saline water is expressed in terms of parts of salt per thousands of parts of water.
The water of the world's oceans has a salinity generally around 35 parts per thousand. This is equivalent to 35 grams of salt per 1 kilogram of water, which occupies roughly 1 liter of volume.
Purified and sterilized sodium chloride in water at a ratio of 9 grams of salt per kilogram of water is known as a saline solution. It is used to rinse eyes and clean contact lenses. As a treatment it is administered intravenously, in cases of dehydration.