What does VACU stand for?

Vacuum

Pressure less than atmospheric pressure. It is usually expressed in inches of mercury (Hg) as referred to the existing atmospheric pressure. A vacuum is a space that has no pressure and no molecules inside. It is truly and empty space. Although space has a very low pressure (almost a vacuum), there are still particles out there. A volume which contains no matter. A completely empty space. The collapsing can experiment shows the effect of the pressure of gas particles.