An AED, or Automated External Defibrillator, is a portable device used to treat people experiencing sudden cardiac arrest. It works by analyzing the heart's rhythm and delivering an electric shock if necessary to restore a normal heartbeat. AEDs are designed for use by laypersons and provide voice prompts to guide users through the process. These devices are commonly found in public places such as schools, airports, and shopping centers, making them accessible in emergencies. Training in CPR and AED use is often encouraged to increase the chances of survival for individuals in cardiac distress.