AED stands for automated external defibrillator.
In more detail, an automated external defibrillator (AED) is a portable electronic device that automatically diagnoses the life-threatening cardiac arrhythmias of ventricular fibrillation and ventricular tachycardia in a patient, and is able to treat them through defibrillation, the application of electrical therapy which stops the arrhythmia, allowing the heart to re-establish an effective rhythm.
Essentially, an AED is used to help people experiencing sudden cardiac arrest. This medical emergency occurs when the heart suddenly stops beating, often due to an electrical problem in the heart. The AED delivers an electrical shock to the heart, which can restore a normal heartbeat.
