What is the lowest type of cloud called?

The lowest type of cloud is indeed stratus. Stratus clouds are characterized by their flat, gray appearance and can cover the entire sky like a blanket, leading to overcast conditions. They typically form at low altitudes, generally ranging from the ground up to about 2,000 meters (6,500 feet) and are associated with light precipitation, such as drizzle.

The context for other types of clouds can further clarify why stratus is the lowest. Cumulus clouds, for example, are puffy and often seen in fair weather, forming at varying heights but usually higher than stratus clouds. Cirrostratus clouds are high-altitude clouds, usually forming above 6,000 meters (20,000 feet), and are known for their thin, ice-crystal structure that can create a halo around the sun or moon. Nimbus generally refers to clouds that produce precipitation, such as nimbostratus, which can be low but are categorized more by their precipitation characteristics rather than altitude alone. Therefore, stratus is accurately identified as the lowest type of cloud due to its typical formation at lower altitudes and distinct flat appearance.