What is Pressure?
Air or atmospheric pressure, is the force exerted on the Earth, by the weight of the air above. That depends on how high the column of air is, so the higher the surface, the less the pressure. That is why you set your barometer to the height of your house or school above sea-level to get correct readings.

Why is it Important?
Different pressure regimes have different types of weather associated with them.

Barometer readings are plotted on a pressure chart. Points on a map that have the same air pressure are connected by lines known as isobars. By studying the patterns shown by isobars, forecasters can make predictions about how the weather will develop. We can identify "troughs" of low pressure and "ridges" of high pressure.