In meteorology, what is the term for the amount of water vapour actually present in the air at a given time?

Introduction / Context:
This question belongs to basic meteorology and weather science. It asks for the term used to describe how much water vapour is present in the air. This concept is important for understanding weather conditions, comfort levels, and phenomena such as fog, clouds, and rainfall.

Given Data / Assumptions:

• The focus is on the amount of water vapour actually present in a sample of air at a particular time.
• Several related terms from meteorology are listed, including saturated air, precipitation, humidity, and capacity.
• The standard terminology used in school and competitive exam syllabi is assumed.

Concept / Approach:
Humidity is the general term for the amount of water vapour in the air. There are more specific related measures, such as absolute humidity, relative humidity, and specific humidity. Absolute humidity is the mass of water vapour per unit volume of air, and relative humidity compares the current water vapour content with the maximum possible at a given temperature, expressed as a percentage. Saturated air refers to air holding the maximum amount of water vapour possible at that temperature, so that any further cooling would cause condensation. Precipitation describes water falling from the atmosphere to the surface as rain, snow, or hail. Capacity refers to the maximum water vapour the air could hold at a given temperature but does not directly state how much water vapour is currently present.

Step-by-Step Solution:

Verification / Alternative check:
You can verify the correct term by listening to or reading weather forecasts. They routinely mention humidity levels, often as relative humidity percentages, to describe how much moisture is in the air. Textbooks on geography and meteorology also define humidity as the amount of water vapour in the atmosphere and then break it down into specific types of measurements.

Why Other Options Are Wrong:

Saturated air is incorrect as an answer to this definition because it describes air that has reached maximum vapour capacity and is on the verge of condensation, rather than a general term for water vapour content.

Precipitation is incorrect because it refers to water in liquid or solid form falling from clouds, not to water vapour still mixed with the air.

Capacity is incorrect because it describes the maximum amount of water vapour that air can hold at a given temperature, not the amount that is currently present.

Common Pitfalls:
Students sometimes confuse humidity with precipitation, thinking both terms simply mean moisture. Others mix up saturated air and humidity, assuming that any mention of water vapour implies saturation. It is important to separate the idea of actual vapour content, which is humidity, from the maximum possible vapour content, which is related to capacity and saturation. Recognising these distinctions helps in interpreting weather charts and understanding dew point and fog formation.

Final Answer:
The term used in meteorology for the amount of water vapour actually present in the air is Humidity.