MDI, or Metered Dose Inhaler, is a device used to deliver medication directly to the lungs. It typically contains a pressurized canister filled with a specific dose of medication, which is released in a fine mist when the inhaler is activated. MDIs are commonly used to treat respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD). Using an MDI requires proper technique to ensure the medication reaches the lungs effectively. Patients must coordinate their inhalation with the release of the medication, often using a spacer device to enhance delivery. Regular use of MDIs can help manage symptoms and improve overall lung function.