A story or event centered around human misery. Characters in the story face suffering, dread, and destruction.
Most tragedies are actually caused by the protagonist themselves. This could have been caused by a wicked deed they committed. Usually the audience can predict if an event will cause a downfall. The downfall can led to many things; death, major death, a handicap, betrayal, loss of wealth, insanity, torture, destruction, the appearance of a fear, depression, or a combination.
Some stories may have a tragic event but may not be tragedies themselves. This is very common in dramas. It may be triggered by a downfall but unlike a tragic story the characters are able to recover and move on.
A common misconception is that all tragedies are also horror stories. This is not always the case. Not all tragedies are horror as not all horrors are tragedies. Some tragedies may be a happy story without any scary elements but ends with an extremely sad manner. While not all horror stories end tragically, some horror stories may actually end with a high note.
Used in other Literature
In the age of Greek plays the two major genres were comedies and tragedies. There were a massive amount of plays about tragedies, some plays even ended with an actual death on stage.
Shakespeare also created many famous tragic story; Romeo and Juliet, Hamlet, King Lear, Macbeth, and Othello. His plays were so famous that their is a genre of tragedy known as Shakespearean Tragedy.
What doesn't make a Tragedy
A tragedy must have an unconquerable downfall. If a character is able to overcome the misery then it is probably not a tragedy.
In some cases a story may have an unconquerable downfall for a main character but it may not be a tragedy. If the character still feels no remorse for previous actions, if the downfall doesn't provide much suffering, or if the audience could never relate to the character throughout the whole story then even with an unconquerable downfall it may not be a tragedy.