If the air is sucked out of a plastic drink bottle, the walls of the bottle buckle inwards. This occurs because the pressure of air on the outside is greater than that on the inside. If all the air is removed from a container, it is said to contain a vacuum (korekore).
An everyday example of this is vacuum packaging. Air that could cause a food to spoil or go stale is removed from the package, and the push (pana) of the air outside causes the packaging to press inwards against the food.