Condensation is the process by which water changes its state from a vapor or gas to a liquid. Condensation is responsible for the formation of clouds. Common examples of condensation are: dew forming on grass in the early morning, eye glasses fogging up when you enter a warm building on a cold winter day, or water drops forming on a glass holding a cold drink on a hot summer day.
Condensation occurs when water droplets form due to cooling air. When warm air cools, water leaves the vapor that is in the warm water and condenses into liquid.
source: windows to the universe