The salinity can simple be defined as the amount of salt that is contained in the ocean waters.
The salinity of the ocean waters comes from the interaction of the chlorine and the sodium which are in abundance. With their interaction the salt is created, or chemically, the NaCl.
The salinity varies from place to place, and it is dependent on multiple factors, with the climate being the most important, backed by the income of freshwater from rivers and streams.
The hotter it is, the higher the salinity, because there's bigger evaporation and the salt concentrates more, and vice versa.
The waters that are near a coast, and there's a stream or a river that constantly bring in freshwater, are less saline, because the freshwater increases the amount of water on the amount of salt, thus it is much more dispersed.
