A millibar is part of the metric system and is a unit of pressure. It is abbreviated by mbar or mb and is derived from the bar.
Both the millibar and the bar from which is was derived are used in meteorology. They were first used by British meteorologist William Napier Shaw in 1909. Millibars are used to express atmospheric pressure when pressure at sea level is defined as 1000 mbar. The millibar is not used universally when describing weather patterns. The hectopascal, symbolized by hPa, is used on Canadian weather maps. In America, the millibar is used when describing the conditions of hurricanes and cyclones.