A vacuum is space devoid of matter. The word is derived from the Latin adjective vacuus meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.

ನಿರ್ವಾತ:ಎಂದರೆ ಯಾವುದೇ ವಸ್ತು ಇರದ ಅವಕಾಶ(space).ವಾಸ್ತವದಲ್ಲಿ ಸಂಪೂರ್ಣ ನಿರ್ವಾತ ಎಂಬುದಿಲ್ಲ. ಏಕೆಂದರೆ ಯಾವುದೇ ಅವಕಾಶದಿಂದ ವಾಯುವಿನ ಎಲ್ಲಾ ಅಣುಗಳನ್ನು ತೆಗೆಯಲು ಸಾದ್ಯವಾಗಿಲ್ಲ.ಆದುದರಿಂದ ಎಲ್ಲಾ ಪ್ರಾಯೋಗಿಕ ಉದ್ದೇಶಗಳಿಗೆ ವಾತಾವರಣದ ಒತ್ತಡದಿಂದ ಕಡಿಮೆ ಒತ್ತಡದ ಮುಚ್ಚಿದ ಅವಕಾಶ(enclosed space)ಗಳನ್ನು ನಿರ್ವಾತ ಪ್ರದೇಶ ಎನ್ನಬಹುದು.