A rescue inhaler is a portable device used to quickly relieve symptoms of asthma or other respiratory conditions. It contains medication, usually a bronchodilator, that helps open the airways, making it easier to breathe during an asthma attack or when experiencing shortness of breath. These inhalers are typically used as needed and are different from maintenance inhalers, which are taken regularly to control symptoms over time. It's important for individuals with conditions like asthma to carry their rescue inhaler at all times to manage sudden breathing difficulties effectively.