In everyday language, this refers to a negative pressure below the atmospheric pressure of 1013 mbar absolute. According to DIN 28400-1, vacuum is defined as “when the pressure of the gas inside a container […] is lower than outside or when the pressure of the gas is lower than 300 mbar, i.e. lower than the lowest atmospheric pressure occurring on the earth’s surface.”

In vacuum soldering, the term vacuum is used as soon as the solderingmaterial is in a bell jar or chamber whose pressure is lower than the atmospheric pressure prevailing in the surroundings.