Condensation

Condensation is the change of water from its gaseous form (water vapor) into liquid water. Condensation generally occurs in the atmosphere when warm air rises, cools and looses its capacity to hold water vapor.

In regards to condensation in your home, when warm air which is full of moisture comes into contact with a wall or window, that is colder than it is, the warm air is unable to retain the same amount of moisture, and the water is released onto the cold surface, this can also happen when warm air and cold air meet, causing condensation which is visible to see to form.