What does vacuum mean (definition) and what is vacuum packaging?

Definition:
a vacuum is a space in which the air pressure is significantly lower than the normal atmospheric pressure or in which virtually no particles (air or gas) are present. The fewer particles there are, the higher the vacuum. 

Vacuum packaging:
vacuum packaging is film packaging from which the air is extracted during closure. The "vacuuming" process removes the oxygen and makes the food, industrial component or other product better storable with a longer shelf life, as well as giving it an attractive appearance for its resale.