A Metered Dose Inhaler (MDI) is a device used to deliver medication directly to the lungs. It contains a pressurized canister that releases a specific dose of medication in aerosol form when activated. MDIs are commonly used to treat respiratory conditions like asthma and chronic obstructive pulmonary disease (COPD). To use an MDI effectively, the user must shake the inhaler, exhale fully, and then press the canister while inhaling deeply. This ensures that the medication reaches the airways effectively. Proper technique is essential for optimal medication delivery and to manage symptoms effectively.