Cabin pressure is a process in which conditioned air is pumped into the cabin of an aircraft or spacecraft, in order to create a safe and comfortable environment for passengers and crew flying at high altitudes.

Earth's atmospheric pressure varies with altitude. At the earth's surface(sea level) , It is measured at 14.7 pounds per square inch(psi) which humans are accustomed to because it provides the optimum amount of oxygen.

As an aircraft ascend to higher altitudes, the atmospheric pressure decreases and oxygen becomes unavailable. Since humans need oxygen to survive, something had to be done to keep the precious lives of people on-board hence, cabin pressure is maintained at appropriate levels.