A Ground Fault Circuit Interrupter (GFCI) is a device designed to protect people from electric shock by quickly cutting off power when it detects an imbalance between incoming and outgoing current, indicating that some current may be flowing through an unintended path such as water or a person's body. It is commonly used in areas where water and electricity might come into contact, like kitchens or bathrooms, providing essential safety in residential, commercial, and industrial settings.