Weather describes the day-to-day condition of the atmosphere. It might be sunny, hot, windy or cloudy, raining or snowing.
The weather takes into account the temperature, precipitation, humidity and atmospheric pressure of the part of atmosphere (air) closest to the surface of the Earth.
The weather is constantly changing as temperature and humidity change in the atmosphere. Landmasses, such as the British Isles, experience constantly changing weather conditions.
The science of monitoring and studying the atmosphere and predicting its weather and climate is called meteorology. People who study the weather and climate are known as meteorologists.