One bar is a measure of atmospheric pressure that is equal to the pressure felt at sea level on Earth. It has largely replaced the older unit of one atmosphere, which is equal to 1.013 bar.
As of 2014, the bar is only partially integrated into the metric system, as the International Union of Pure and Applied Chemistry has defined 1 bar as being exactly equal to 100,000 pascals. The bar, and the smaller millibar, are most commonly used in meteorology and for industrial applications like the calibration of hydraulics. The bar is recognized for official use by the European Union, though the International Astronomical Union prefers the use of kilopascals and megapascals.