The gaseous state of water is referred to as "vapour." In this state, water molecules are in the form of a gas rather than a liquid or solid. Understanding the different states of water is crucial as it helps us comprehend various natural phenomena like the water cycle, cloud formation, and weather patterns.

The gaseous state of water is represented by "vapour" because it is formed when liquid water molecules gain enough energy to overcome the attractive forces between them and escape into the air as gas molecules. This process is known as evaporation.

Below are the key points to explain the answer:

1. Understanding the states of matter:
- Matter can exist in three main states: solid, liquid, and gas.
- In the solid state, particles are tightly packed and have a fixed shape and volume.
- In the liquid state, particles are more loosely packed and have a definite volume but no fixed shape.
- In the gaseous state, particles are widely spaced and have neither a fixed shape nor volume.

2. Water's different states:
- Water can exist in all three states: solid, liquid, and gas.
- In its solid state, water is called "ice." Ice has a fixed shape and volume.
- In its liquid state, water is the common form we encounter, with a definite volume but no fixed shape.
- In its gaseous state, water is referred to as "vapour." Water vapour has neither a fixed shape nor volume.

3. Formation of water vapour:
- When liquid water gains enough energy, its molecules start moving faster.
- As the molecules move faster, some gain sufficient energy to break free from the liquid's surface and escape into the air.
- These molecules become water vapour and mix with the surrounding air.
- This process is called evaporation and occurs at any temperature, although it is faster at higher temperatures.

4. Importance of water vapour:
- Water vapour plays a crucial role in the water cycle.
- It rises into the atmosphere and condenses to form clouds.
- Clouds are made up of tiny water droplets or ice crystals, which eventually fall as precipitation, such as rain, snow, or hail.
- This precipitation replenishes water sources on Earth, allowing the water cycle to continue.

In conclusion, the gaseous state of water is known as "vapour." Water molecules in this state exist as a gas and mix with the surrounding air. Understanding the different states of water is important for comprehending natural phenomena like the water cycle and cloud formation.