I used to think weather was the condition of the atmosphere at a certain time and place. It is always changing and effects our everyday life. Wind, one type of weather, is caused by the uneven heating of the Earth that causes pressure changes. Precipitation, another type of weather, is caused by the water cycle, after water evaporates, condenses into clouds, and is then pulled down.
Now I think weather is the condition, temperature, pressure, moisture and density of the air. Weather is caused by the way air masses moves in accordance to other air masses. There are many different types of weather, from snow to really hot air to wind, and they are all caused by many different movements in the air.