Water in its gaseous state, especially in the atmosphere and at a temperature below the boiling point. Water vapor in the atmosphere serves as the raw material for cloud and rain formation. It also helps regulate the Earth's temperature by reflecting and scattering radiation from the Sun and by absorbing the Earth's infrared radiation.
Water in a gaseous state, especially when diffused as a vapor in the atmosphere and at a temperature below boiling point.
Water vapor is steam.
An example of water vapor is the floating mist above a pot of boiling water.