Hypotonic comes from the Greek "hypo," meaning under, and "tonos," meaning stretching. In a hypotonic solution the total molar concentration of all dissolved solute particles is less than that of another solution or less than that of a cell.
If concentrations of dissolved solutes are less outside the cell than inside, the concentration of water outside is correspondingly greater. When a cell is exposed to such hypotonic conditions, there is net water movement into the cell. Cells without walls will swell and may burst (lyse) if excess water is not removed from the cell. Cells with walls often benefit from the turgor pressure that develops in hypotonic environments.