Moist air refers to air that contains water vapor, which is the gaseous form of water. The amount of moisture in the air is measured as relative humidity, indicating how much water vapor is present compared to the maximum amount the air can hold at a given temperature. Warm air can hold more moisture than cold air, making humidity levels fluctuate with temperature changes. The presence of moisture in the air affects various properties, including temperature, pressure, and density. Higher moisture levels can lead to increased heat retention, making humid conditions feel warmer. Additionally, moist air can influence weather patterns and contribute to phenomena like cloud formation and precipitation.