The correct term for water occurring in the air as an invisible gas is water vapour. Water vapour is the gaseous state of water and is present in the air around us. It is formed when liquid water evaporates and turns into a gas. Water vapour is invisible to the human eye and can only be seen when it condenses into visible droplets, such as clouds, fog, or dew. Water vapour plays a crucial role in the water cycle and is essential for various atmospheric processes, including precipitation and cloud formation.