The meaning of "tragedy" had changed over the past 2500 years from the definition of the original Greek word. Today, the word “tragedy” usually denotes some sort of devastating occurrence (e.g., the bombing of the World Trade Center), but originally the word was used in reference to a specific type of dramatic art form in which a playwright represents a person or group of persons, primarily the nobles of mytholgy, as experiencing a reversal of fortune from good to bad. Such reversals of fortune create feelings of pity and fear in the audience. For the most famous definition of tragedy, please see Aristotle’s Poetics.
In Euripides’ Medea, for example, we witness the fall of Jason, as well as the deaths of his sons, King Creon of Corinth, and Princess Glauce of Corinth at the hands of Medea, who is furious that Jason is divorcing her to marry the princess. In Sophocles’ Oedipus the King, the playwright depicts the fall of Oedipus, King of Thebes, when he discovers that he has unwittingly killed his father and married his mother. So, whereas events such as the bombing of the World Trade Center or Hurricane Katrina are tragic and certainly do cause feelings of pit and fear, they are not tragedies in the original Greek sense of the word.