What is a definition of a vacuum?

A vacuum is defined as the absence of matter. This encompasses not just air, but any particles or substances that may be present in a given volume. In a vacuum, there are no atoms or molecules, resulting in significantly low pressure and density, which is why vacuums can be utilized in various scientific and industrial applications, like creating conditions for experiments in physics or maintaining certain manufacturing processes.

The other definitions refer to specific aspects that may be present in a vacuum. While a vacuum can lead to a lack of air and low pressure, these are not comprehensive enough to define what a vacuum is. Likewise, sound cannot propagate in a vacuum due to the absence of matter, but this characteristic is merely a consequence of the vacuum, not a defining feature. Thus, the most accurate and broad definition pertains to the absence of all matter.