A parable is generally a tale of varying length which illustrates or advocates a certain moral or lesson. Most commonly the word is used to refer to stories from the Christian Bible, written not for informational purposes but rather to convey a model of religious behavior. Typically biblical parables fall into one of five categories and most are comparative in nature, which instills an ethic of empathy.
Similes
The shortest type of a parable is a simile, a simple comparison utilized throughout literature with "like" or "as" being the transitory word.
Similitude
A similitude is a lengthened simile, using a more complex description to illustrate the contrast.
Extended Comparisons
Extended comparisons are even longer parables than similitudes, but they still do not take on any kind of narrative form to teach their lesson.
Narrative Parables
Narrative parables contain a visible story arc that develops characters and demonstrates in detail the impact of the plot upon the characters.
Example Stories
Example stories make no comparison between two groups of people or sects of society but instead directly provide a clear example of behavior that should be followed or avoided in a certain situation. Perhaps the most well-known example of an example story is the tale of the Good Samaritan, in which a Samaritan assists an injured Jew. The two were considered enemies by society, and the story teaches the distinctive "love your neighbor" ethic of Christianity.
Non-Christian Parables
Almost every religious text contains parables of some kind which seek to reinforce the meaning of scripture. There have been cases in modern literature of stories referred to as parables for their moral advocacy. The science fiction novelist Octavia Butler has written a "Parable" duology.