Technically speaking, clouds are the evidence of rising air masses and condensing water vapor. Weather forecasters and observers can deduce current and future weather events based on cloud shapes. Aesthetically speaking, the infinite variety and beauty of clouds have delighted us since the beginning of man. Surprising, a system for classifying clouds did was not developed until the early 19th century.
In 1803, English scientist Luke Howard presented a classification scheme to his local scientific society. Using the language of science--Latin--Howard classified the basic cloud shapes. His system allowed for words to be combined which enabled further classification. His system was immediately accepted and universally admired.
Today's classification system begins with two basic types: cumuliform and stratiform. Cumuliform is taken from the Latin word cumulus, which means heap. Cumuliform clouds are puffy clouds. This type is usually formed from convection or orographic lifting.
Stratiform is taken from the Latin word stratus, which mean layer. Stratiform clouds have a flat, layered shape. Stratiform clouds result from uniform lifting usually associated with frontal systems. Stratiform clouds are generally accompanied by stable weather.
These two basic types can be further classified by the height at which they form. High-level clouds (above 16,500 feet) are called cirrus clouds. Sometimes the prefix cirro- is added to a basic cloud type. Clouds forming between six,500 and 16,500 feet take the prefix alto-. Clouds forming below Six,500 feet have no prefix, so the basic types (stratus and cumulus) refer to low level clouds by default. By combining height prefixes with basic types, you can describe several types of clouds. For example, altostratus refers to a layer cloud at mid-level altitudes.
The familiar cumulonimbus cloud is in a category by itself, because it extends from low to high altitudes. The word nimbus means rain-bearing.
Cloud classification is not an exact science. But since clouds are infinitely and constantly variable, a flexible cloud classification system may actually work most outstanding.