- Vacuum (partial): A realizable vacuum with a gaseous pressure that is much less than atmospheric.
- Vacuum (classical): The term classical vacuum as used in classical electromagnetism and in the definition of the SI units refers to an ideal reference medium devoid of all particles, with ideal properties. These ideal properties include: independence from field strengths, direction, frequency, or polarization, and from temperature.
- Vacuum (quantum electrodynamic): The term quantum electrodynamic vacuum, or QED vacuum, refers to the ground state of the electromagnetic field, which is subject to fluctuations about a dormant zero average-field condition.
- Vacuum (political): A situation in which no power is dominant, and the power balance is in flux.
- Vacuum distillation: The laboratory or industrial-scale distillation of liquids performed at a pressure lower than atmospheric pressure.