Containment means keeping something confined within limits so it can't spread or grow larger. When a forest fire breaks out, firefighters work to achieve containment by creating barriers that prevent the flames from spreading to new areas. Doctors try to contain an outbreak of illness by isolating sick patients so the disease doesn't spread through a hospital.

The word suggests active effort to hold something back or restrict it. A broken water pipe might be contained with sandbags and tarps. In your classroom, if one student's disruptive behavior starts affecting others, a teacher might work to contain the situation before it spreads. When scientists study dangerous microorganisms, they use special containment facilities with sealed rooms and filtered air to ensure nothing escapes.

During the Cold War, American leaders developed a policy called containment to prevent communism from spreading to new countries. Rather than direct military confrontation, the strategy focused on supporting countries threatened by communist expansion, using diplomacy, economic aid, and sometimes military assistance to keep communism within its existing borders.

The related word contain works as a verb: you might contain your excitement before a surprise party, or a bucket might contain water. Notice how both meanings involve holding something within boundaries, whether those boundaries are physical walls, geographic borders, or even your own self-control.