In physics, the term "vacuum" refers to a region of space that is devoid of matter. It is the absence of particles, such as atoms, molecules, and subatomic particles, within a particular region.
However, it's important to note that a perfect vacuum, where there is absolutely nothing present, is difficult to achieve in practice. Even in so-called empty space, there are still trace amounts of particles and energy fluctuations. These fluctuations are a consequence of the inherent uncertainty and quantum nature of the vacuum at microscopic scales.
In terms of pressure, a vacuum is typically associated with a low pressure compared to its surroundings. In everyday language, we often think of a vacuum as a region with zero pressure. However, in physics, a vacuum can have varying degrees of pressure, depending on the context.
Regarding light, a vacuum is not the absence of light per se. In fact, light can propagate through a vacuum. It does not require a medium to travel through, unlike sound waves, which need a medium like air or water. In empty space, light can move freely without any obstruction. So, a vacuum does not mean the absence of light, but rather the absence of matter.
In summary, a vacuum refers to a region of space that lacks matter, such as particles and atoms. While a perfect vacuum is challenging to achieve, a vacuum is typically associated with low pressure compared to its surroundings. Light can propagate through a vacuum without the need for a medium.