How a vacuum is defined in physics and everyday language has slightly different meanings but core idea is space with little or no matter. In physics, a vacuum is defined as a space devoid of matter, where pressure is much lower than atmospheric pressure, with perfect vacuum being space with zero particles and zero pressure, which does not exist naturally except as theoretical ideal, while practical vacuum is space with very low pressure, such as outer space which is near-perfect vacuum with few atoms per cubic meter. In engineering, vacuum is defined by pressure levels: low vacuum around 760 to 25 torr, medium vacuum 25 to 1e-3 torr, high vacuum 1e-3 to 1e-9 torr, and ultra-high vacuum below 1e-9 torr. In everyday language, vacuum is defined as state of suction or empty space created by removing air, as in vacuum cleaner that creates low pressure area to suck air and dirt inside, or vacuum sealed package. Colloquially, vacuum can also mean empty space or void. So definition ranges from scientific absence of matter to practical low-pressure region used for cleaning or industrial processes, characterized by pressure measurement relative to atmosphere.
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