The process of condensing, or condensation, occurs when a gas is cooled so much that it turns into a liquid.

Water vapour is one of many gases in the air. If the air becomes too cold some of the water vapour changes into a liquid and condenses. For example, on a cold morning you may breathe out moist air from your lungs and white mist may form for a moment in front of your face. This mist is warm moist water from your lungs that has cooled in the cold morning air and immediately changed from vapour to water droplets.

However, condensation also happens with hot gas as it cools. When a kettle or a saucepan boils, water is given off in the form of invisible gas. But as it rises from the kettle or saucepan, it goes into cooler air and the gas then condenses into little droplets. That is called stream by many people, although steam is really invisible. What most people call steam is a tiny cloud cause by the steam condensing into droplets in the air. If you want to prove this, just look at the 'steam' coming out of a kettle (don't get too close!) and you will see that it is invisble just by the spout. That is where the real steam - invisible gas is. The bit you can see as 'steam' is where condensation has taken place.