Which of the following is not a type of cloud classification?

Stratiform is not a recognized type of cloud classification in meteorology. The term typically refers to a type of cloud formation or arrangements, relating more to the structure and appearance of clouds rather than being an established cloud type itself. In meteorology, cloud classification is primarily based on characteristics such as their appearance and altitude.

Stratus, cumulonimbus, and cirrus are all specific types of clouds. Stratus clouds are low, gray, and often cover the entire sky. Cumulonimbus clouds are tall, vertically developed clouds associated with thunderstorms. Cirrus clouds are high-altitude clouds that appear wispy and thin. Thus, the answer highlights the distinction between recognized cloud types and associated descriptors like "stratiform," which does not fit the classification system used to categorize clouds.