Here's a breakdown:

Shape:

* Cirrus (Ci): High-altitude, wispy clouds made of ice crystals. They often look like feathers or strands of hair.

* Cumulus (Cu): Puffy, cotton-like clouds that often have flat bases. They form when warm, moist air rises.

* Stratus (St): Flat, layered clouds that can cover the entire sky. They often bring drizzle or light snow.

Altitude:

* High clouds (above 6,000 meters): Cirrus, Cirrocumulus (Cc), Cirrostratus (Cs)

* Middle clouds (2,000-6,000 meters): Altocumulus (Ac), Altostratus (As)

* Low clouds (below 2,000 meters): Stratus, Stratocumulus (Sc), Nimbostratus (Ns)

* Vertically developed clouds: Cumulus, Cumulonimbus (Cb)

Composition:

* Water clouds: Made of liquid water droplets.

* Ice clouds: Made of ice crystals.

* Mixed clouds: A combination of water droplets and ice crystals.

Other factors considered:

* Cloud cover: How much of the sky is covered by clouds.

* Precipitation: Whether the cloud is producing rain, snow, or other forms of precipitation.

Cloud classification system:

The most widely used cloud classification system is the International Cloud Atlas, which has been revised multiple times since its first edition in 1896.