There are four categories of clouds: high clouds, middle clouds, low clouds, and multi-layer clouds.

High Clouds
These are clouds with bases starting at an average of 20,000 feet.
Cirrus: thin feather-like crystal clouds.
Cirrostratus: thin white clouds that resemble veils.
Cirrocumulus: thin clouds that appear as small "cotton patches."

Middle Clouds
These are clouds with bases starting at about 10,000 feet.
Altostratus: grayish or bluish layer of clouds that can obscure the Sun.
Altocumulus: gray or white layer of patches of solid clouds with rounded shapes.

Low Clouds
These are clouds with bases starting near Earth's surface to 6,500 feet.
Status: thin, gray sheet-like clouds with low base; may bring drizzle and snow.
Stratocumulus: rounded cloud masses that form on top of a layer.
Cumulus: fair-weather clouds with flat bases and dome-shaped tops.

Multi-Layer Clouds
These are clouds that are developed vertically.
Nimbostratus: dark, gray shapeless cloud layers containing rain, snow, and ice pellets.
Cumulonimbus: large, dark, vertical clouds with bulging tops that bring showers, thunder, and lightning.