An airlock is a special chamber used in spacecraft and some buildings to control the movement of people and objects between different environments, such as from outer space to the interior of a spacecraft. It helps maintain pressure and prevents the loss of air or contamination when the outer door is opened. In space missions, airlocks are essential for astronauts to conduct spacewalks or repairs without exposing the spacecraft to the vacuum of space. They are also used in laboratories and cleanrooms to ensure that sensitive areas remain uncontaminated by outside air or particles.