A cloud is a region of condensed moisture. When water is in the liquid state it is much easier to see than when it is in the gaseous state. When air rises it cools. Cooling air results in the air coming closer to saturation. Once the air cools enough the gaseous water will condense into liquid water drops. When saturated air cools the moisture condenses out similar to the way in which you will see moisture develop on the outside of a glass of ice-water.

When air is sinking it will be a nice day outside with sunny skies. An important ingredient to develop a cloud is rising air. Air can rise in a similar fashion to how a helium balloon rises. The air rises since it is lighter than the surrounding air. The air within a cloud is lighter than the air outside of the cloud. What makes the cloud lighter is due to the gaseous water and/or the warmer temperature within the cloud. Gaseous water is less dense than air. When air is warmer it expands. Warmer air is less dense. If you wonder what it is like to be in a cloud then wait for a foggy day.

Below are some of the common clouds you will see and what they look like:

Cirrus- The general term for high clouds composed of ice crystals. They have a feathery and wispy appearance.

Cumulus- The general term for vertically developing clouds. They have a lumpy appearance and develop within an unstable layer in which the cloud can build due to rapidly rising air.

Stratiform / Stratus- The general term for horizontal clouds that develop due to forced uplift. They have a flat appearance and develop within a stable layer.

Fog- Fog is a cloud that has the base on the earth's surface.