Curing is the period after paint dries to the touch when it continues to harden and build in strength. A coat can look finished long before it has cured, which is why we give surfaces their full cure time before scheduling a final walkthrough.
Cure times vary by product and season. Humidity, temperature, and airflow all change how quickly a coat reaches full hardness, so washing a freshly painted wall a week in is still asking for trouble. Patience here protects the finish for the years that follow.