A vacuum is a physical space with no or very little gas molecules and atoms in it. It is a field space where only a variety of energy particles exist. In applied physics and technical applications, vacuum refers to a given space with pressure of the gas state lower than a standard atmospheric pressure. While a perfect vacuum is a totally empty space with no gas, relative vacuum is a gaseous state measured based on the standard atmosphere pressure.
FROM：https://www.landvac.net/
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