Cloud (meteorology)

A visible mass of tiny liquid-water droplets, ice crystals, or both suspended in the atmosphere. Clouds form when water vapor condenses or deposits onto atmospheric particles.

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Cloud condensation nuclei: Tiny airborne particles on which water vapor condenses to form cloud droplets. They provide surfaces for droplets to form when air becomes saturated.
Cloud genus: A primary category in the international system for classifying clouds by form and structure. Clouds are grouped into ten genera, such as cirrus and stratus.
Cloud cover: The fraction of the sky obscured by clouds at a particular time and place. Forecasters use it to describe sky conditions and estimate incoming sunlight.
Precipitation: Water released from clouds that falls to Earth's surface as rain, snow, sleet, or hail. Cloud particles grow large enough to fall and supply precipitation.
Fog: A cloud of tiny water droplets or ice crystals at Earth's surface that reduces visibility. Fog has cloud-like particles but forms at ground level.
Saturation (atmosphere): The state in which air holds as much water vapor as it can at a given temperature and pressure. Clouds commonly begin when cooling brings air to saturation.
Cloud base: The lowest level of a cloud where its visible body begins. Its height helps distinguish cloud types and indicates the lifting condensation level.
Cloud classification: The systematic grouping of clouds by their form, height, and structure. Standardized names let observers communicate cloud conditions consistently.
Earth's energy budget: The balance between energy Earth receives from the Sun and energy it reflects or emits to space. Clouds reflect sunlight and absorb and emit infrared radiation.
Haze: Reduced atmospheric visibility caused by suspended particles, often dry aerosols or pollutants. Haze can look cloud-like but does not consist of a visible cloud body.