The two units of air pressure used in meteorology are low pressure and high pressure. These two units of barometric pressure have a large influence with the weather on Earth.
A low pressure rotates counterclockwise and forces air in an upward direction in the Northern Hemisphere, which causes air moisture to condense, creating rain and sometimes thunderstorms. A high pressure rotates clockwise and forces the air to sink, which usually creates pleasant weather conditions, including clear skies for the surrounding area. In the Southern Hemisphere, these pressures spin in the opposite direction and have the opposite effect as they do north of the equator.