Absolute vacuum is a theoretical state of space that contains no matter and no pressure. It is defined as a complete absence of all gas molecules, including the smallest trace gases. In practice, achieving absolute vacuum is impossible since there are always some gas molecules present, even in the best vacuum systems. However, vacuum pumps can remove most of the gas molecules from a closed chamber, reducing the pressure to a very low level.
The lowest pressure that can be achieved in a vacuum system is known as the ultimate vacuum, which is limited by the residual gas pressure from outgassing of the system components and the vacuum chamber walls. Absolute vacuum has many important applications in scientific research, including in the study of particle physics, astronomy, and vacuum technology.