Brine, in the scientific sense, is water that is so saturated with salts (and other dissolved minerals), that the salt concentration exceeds that of ordinary sea water or ocean water. Typically, sea water has a salt concentration ranging from 35 to 50 parts per thousand (ppt), while brine has a salt concentration greater than 50 parts per thousand (ppt).

Natural examples of brine include the waters of the Dead Sea (formerly named Salt Sea), Mono Lake and Great Salt Lake. Man-made or artificial brine would be water that is salinated until it becomes saturated with salt, exceeding 50 ppt, for cooking, cleaning, etc.

Brine creates an unsuitable environment for most organisms, including fish. Few organisms, however, are capable of tolerating and surviving the high salinity of brine. Such organisms, called halophiles, include certain species of bacteria and algae. A few other types of wildlife, such as certain species of brine fly, brine shrimp and flamingos are also capable of, not only tolerating brine, but thriving on it.