A ghost is the spirit of a person who's died. In most stories and myths, ghosts are pale, translucent, and wispy.
Throughout history, the idea that a person's soul or spirit can remain visible after her death has been common. Some of us long to see the ghost of a loved relative, while others are terrified of the very idea. From this main idea, the word ghost has also come to mean the hint or shade of something: "The ghost of a smile remained on her lips." The Old English root is gast, "spirit," and also "breath."