Compressed gas

Compressed gas is a kind of gas that is squished into a small container, like a can or a balloon. When gas particles are put really close together into a small space, they have to stay close together no matter what. When that container is opened, the gas quickly spreads out or 'expands' since the particles can't stay squished together anymore. For example, when you open a can of whipped cream, the gas quickly spreads out into a lot of tiny droplets on top of your dessert.