The cirrus, altostratus, and cumulus are examples of cloud types. Wave clouds and hole-punch clouds are unusual clouds that appear rarely. Clouds are classified according to their form and height above the sea level.
Clouds below a base of 2,000 meters bear no prefix to their names. Stratus, fog, cumulus, stratocumulus, cumulonimbus and nimbostratus fall into this category.
Mid-level clouds lie at a base between 2,000 and 6,000 meters and are designated by the "alto-" prefix. The altostratus and altocumulus are examples of mid-level clouds.
Clouds at a base above 6,000 meters belong to the high clouds category and are designated by cirrus or "cirro-" prefixes. Examples include cirrus, cirrostratus and cirrocumulus.