A cell is in ISOTONIC SOLUTION when solute concentrations inside and outside the cell are equal.
When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell.
Other movement of water in the cells are hypotonic solution and hypertonic solution. Hypotonic solution is where concentration of dissolved solutes are less outside the cell than inside it. Hypertonic solution is where concentrations of dissolved solutes are greater outside the cell than inside it.