An airlock is a sealed chamber that allows for the transfer of people or objects between two environments with different pressures or atmospheres. Commonly used in spacecraft, submarines, and clean rooms, airlocks help maintain the integrity of the internal environment by preventing contamination or pressure loss. When someone enters an airlock, they first close the outer door, which allows the airlock to equalize pressure before opening the inner door. This process is crucial in settings like space exploration or laboratories, where even small changes in pressure or contamination can have significant consequences.