I’ve come across this term and searched it in Wikipedia. According to Wikipedia,

An automated external defibrillator or AED is a portable electronic device that automatically diagnoses the potentially 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 reestablish an effective rhythm.

This piece of device can truly be a lifesaver to those with heart problems. I’ve read that in some countries they even have AEDs placed in the public places .