Where ever sodium goes something follows it by a specific process. What is this and what is the definition?

Answer 1

I think you mean in the human body--since this is in the health section. Anyway, If you're referring to when the sodium level in the fluid outside a cell membrane is higher (or lower) that inside the cell membrane, the cell--through "osmosis"--tries to equalize the salinity by taking in (or sending out) fluids.

Answer 2

Osmosis. The tendency of fluids to pass through a semi-permeable membrane and become mixed in equal strength. (as a saline solution.)