Isotonic

osmotically equal to human cells

An isotonic solution (e.g. a 0.9% solution of sodium chloride) has an osmotic pressure that is equal to the osmotic pressure of the human blood (7.5bar). In this equilibrium the cells and the solution contains an equal concentration of impermeable solutes that are osmotically active. Thus there is no fluid shift between the compartiments (in or out of the cells).

Specifications like "isotonic" on sport drinks, refer to this value.