“The vacuum is an experimentally attainable state”, as it is defined in physics. By vacuum, we mean a space completely void of matter, "called absolute vacuum".In practice, this state is unattainable, so when we say vacuum, we mean that the air pressure inside an environment is lower than atmospheric pressure, or when the density of the particles in the air is lower. With the expressions "Vacuum", "suction", "negative pressure", etc., we are referring to a pressure below atmospheric pressure, due to the weight of the overlying air. At sea level, this pressure is equal to 1013 mBar....
Technology for vacuum applications