Sea-Level Pressure
Because pressure varies with altitude, it is difficult to compare pressures around the globe that are a result of weather conditions. Altitude corrections are made so that pressure observations taken at one location can be compared at those taken at another. Pressure values are adjusted to an altitude of 0 meters, called mean sea level pressure.
Source: Introduction to Tropical Meteorology | UCAR
Because pressure changes with temperature, sea-level pressures of specific locations change with the seasons. This map shows mean sea level pressures during the month of July. Where are areas of high and low pressures?