pressurized

An object or system that's pressurized has air or gas inside it at a certain level of pressure.

When we talk about something being pressurized, usually we're referring to objects like airplanes or scuba tanks. These things need air pressure to function correctly - for example, the oxygen in an airplane cabin is pressurized so that people can breathe easily while flying high above sea level. Pressurization also applies to storage containers, like large metal boxes used for shipping goods.