Turgidityis a cellular state in which a plant cell, having absorbed water, is in a state of tension. The opposite state is plasmolysis.
Turgidity is due to the entry, by osmosis, of a flow of water into the plant cell and its vacuole. The pressure created by this flow of water, or turgor pressure, rigidifies the soft parts of the plant (stems, leaves, petals).
This flow of water is created by the presence, in the external environment, of a liquid that is less concentrated than the cellular environment, which causes the movement of water by osmosis from the external environment into the cellular environment.
Thus, the cells of a plant suffering from hydric stress and wilting due to the lack of water, swell in the presence of water and return the plant its developed posture.
Diagram of turgidity and plasmolysis in a plant cell depending on water flow. © Svtsvt, Wikimédia CC by-sa 3.0