To ventilate means to allow fresh air to flow into and through a space, replacing stale or stuffy air. When you open windows on opposite sides of your house to create a breeze, you're ventilating. Schools ventilate classrooms through heating and cooling systems that constantly bring in outdoor air, keeping the air fresh even when windows stay closed.

Good ventilation matters because air can become stale, humid, or full of odors when it sits still too long. Old houses often had high ceilings and transom windows above doors specifically to improve ventilation before air conditioning existed. Greenhouses use vents to control temperature and humidity. Even your computer has vents to let hot air escape so the electronics don't overheat.

In medicine, doctors sometimes need to ventilate a patient's lungs using a machine called a ventilator, which helps someone breathe when their body can't do it well enough on its own.

The word can also mean to express feelings or opinions openly. Someone might ventilate their frustration by talking through what's bothering them.