MDI, or metered-dose inhaler, is a device used to deliver medications directly to the lungs for the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. Synonyms for MDI include inhaler, puffer, aerosol inhaler, and pressurized inhaler. Inhaler is the most commonly used synonym for MDI, as it is a broad term that covers different types of inhalers used for respiratory treatment. Puffer is another synonym frequently used, referring to the mechanism used to deliver the medication in a measured dose. Aerosol inhaler and pressurized inhaler both refer to the specific technology used in the inhaler to create the mist of medication that is inhaled into the lung.