What is humidity?

Hint: Humidity tells about the amount of moisture present in the atmosphere. We can understand humidity with some daily examples like the clothes take longer time to dry on a high humid day.

Complete answer:
Humidity is a measure for moisture present in the atmosphere. When we say moisture, we mean the water vapours present in the air. This means that humidity tells us about the amount of water vapours present in the air. Water vapours are the gaseous form of water.
There is on more term called relative humidity. Relative humidity is measured in terms of percentage. It tells us how close the air to being saturated with the water vapours. The relative humidity depends on the temperature.
If the amount of water vapours remains the same but the temperature increases then the relative humidity decreases.
If the amount of water vapours remains the same but the temperature decreases then the relative humidity increases.
Let us discuss how humidity affects the surroundings.
When we are warmer or sweaty, we say that the humidity is high. Therefore, when the humidity outside is high we feel warmer.
On a high humid day, our clothes do not get dry at a faster rate than that of a low humid day. Thus, the humidity affects the rate of evaporation. High humidity lowers the rate of evaporation.

Note:
It is sometimes misunderstood that when the amount of water vapours present in air is high we should feel colder. Therefore, let us make it clear with the following explanation.
On hot sunny days, when we sweat, the sweat evaporates and we feel cool. We already know that the rate of evaporation of the sweat depends on the amount of water vapours present in the air. Therefore, when the humidity is high the sweat does not evaporate quickly and thus we feel hot and sticky.