Humidity is the amount of water vapor in the air. It affects comfort, clouds, rain, fog, drying, and how hot or cold air feels.
Relative humidity
Relative humidity compares how much water vapor is in the air to how much the air could hold at that temperature. Warm air can hold more water vapor than cold air.
Humidity and comfort
High humidity can make hot weather feel hotter because sweat evaporates more slowly. This connects closely with the heat index.
Humidity is not rain by itself, but it is one ingredient in many weather conditions.