Power Pellet, also known as an Energizer, is an object used in the Pac-Man games.
When Pac-Man devours a Power Pellet, it causes the ghosts to become vulnerable, allowing him to eat them. After the ghosts are eaten, only their eyes remain and they go back to the center of the maze to regenerate. If the ghosts don't get eaten during that time, they will turn back to normal.
