To contain means to have something inside or to hold something within limits. A backpack contains your books and lunch. A glass jar contains marbles. Your house contains all the furniture and belongings your family owns. When a box contains something, that thing is inside the box.

The word also describes keeping something from spreading or getting worse. Firefighters work to contain a wildfire by creating barriers so it doesn't spread to new areas. A teacher might contain her laughter when a student tells an accidentally funny story during a serious moment. Doctors try to contain an outbreak of illness by preventing it from reaching more people.

Sometimes contain means to hold back strong feelings or reactions. If you contain your excitement about a surprise party, you're keeping yourself from showing it too obviously. A student might struggle to contain their disappointment after losing a close game.

A container is anything designed to hold things: bottles, boxes, bags, or bins. The related word self-contained describes something complete on its own, like a self-contained classroom that has everything students need without leaving the room.