Hey LoST RaiNDRoP,
A spoiler is a major plot point to someone who hasn't seen the show/movie yet. Example: Someone has never seen the original movie "Star Wars". A spoiler for that could be:
Star Wars spoiler wrote:In the middle of the movie, Obewan is killed by Darth Vader so that Luke, Leia, and the rest can excape from the Death Star.
OR
Darth Vader is actually Luke Skywalker's father.
Mentioning something like that to someone who hasn't seen the movie could effectively "spoil" the movie for them since they already know what is going to happen.
Unfortunatly, most modern movie trailers are just a bunch of spoilers. I really really really wish they didn't say "I see dead people" in the trailer for Sixth Sense. That would have made the first half of the movie MUCH more enjoyable.
Anyways, I hope this helps. Good luck and have fun!! ^_^
Phade.