1. Defining Humidity:
Humidity is the general term used to describe the amount of water vapor present in the air.
2. Specific Types of Humidity:
• Absolute Humidity: The actual mass of water vapor per unit volume of air ($g/m^3$).
• Relative Humidity (%): The ratio of the current amount of water vapor in the air to the maximum amount the air could hold at that specific temperature. This is the most common value cited in weather reports.
3. Why other options are incorrect:
• Density: The mass of air per unit volume.
• Viscosity: The measure of a fluid's resistance to flow (internal friction).
• Temperature: The measure of the average kinetic energy of the particles in the air.
Therefore, humidity is the precise scientific term for the moisture content of the atmosphere.