Negative pressure refers to the condition where the pressure inside a given area is lower than the atmospheric pressure outside. This condition can be described using a number of different synonyms which include vacuum, suction, reduced pressure, low pressure, and partial vacuum. Vacuum refers to a completely empty area where there are no air molecules while suction is a term that describes the action of air being drawn into a low-pressure area due to differences in air pressure. Reduced pressure and low pressure are both used to describe pressure that is lower than the atmospheric pressure. Finally, partial vacuum denotes a situation where there is a combination of low pressure with some air molecules present in the environment.