Pressure systems are large-scale weather patterns that influence atmospheric conditions. They are categorized into two main types: high-pressure systems and low-pressure systems. High-pressure systems are associated with clear skies and calm weather, while low-pressure systems often bring clouds, rain, and storms. These systems are driven by temperature differences in the atmosphere, which create variations in air density. As warm air rises, it creates a low-pressure area, while cooler air sinks, forming high-pressure zones. Understanding pressure systems is crucial for meteorologists to predict weather changes and patterns effectively.