Clouds are one form of condensation. They are best described as visible aggregates of minute droplets of water or tiny crystals of ice. Clouds form from water that has evaporated from lakes, oceans, and rivers, or from moist soil and plants. This evaporated water, called water vapour, expands and cools as it rises into the air.
Air can hold only a certain amount of water vapour at any given temperature.
When the temperature drops, some of the water vapour begins to condense into tiny droplets of water or tiny crystals of ice. Most rain originates in either nimbostratus clouds or in towering cumulonimbus clouds that are capable of producing unusually heavy rainfalls known as cloudbursts .