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Merriam Webster online has this to say:

"An outcome in which vice is punished and virtue rewarded usually in a manner peculiarly or ironically appropriate".

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=poetic+justice

Yeah, "peculiarly or ironically appropriate". Take the scene in The Return of the Jedi where Boba Fett falls into the buried monster's gullet on Tatooine: That is poetic justice, and the only reason we expect it to happen is that poetic justice of that sort ("bad guy hoist by own petard") is a cliché in action movies.

Half the people who talk about "poetic justice" nowadays haven't a clue what it means. You can use the term however you like, of course. You can also say "horse" when you mean "lawnmower". Hell, you can just stand there and grunt, if that's what turns you on. You'll be communicating just as effectively.