When the concentration is equal, the plant cell still doesn't have enough pressure. Theturgor pressure provided by osmosis in a hypotonic solution pushes outward on the plant cell wall, which is just what the plant cell needs to maintain its structure.  Osmosis is the movement of solvent molecules through a semi permeable membrane.

Turgor is primarily a botanical term. 
Turgor pressure IS osmotic pressure against the cell wall of a plant cell. 
This pressure may cause a slight swelling of a plant cell. 
An animal cell might burst with with too much osmotic because it lacks a rigid cell wall. 
Plants deficient in turgor pressure are said to be "wilting."